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1
Munroe, Jeffrey S., Emily C. Attwood, Samuel S. O'Keefe, and Paul J. M. Quackenbush. "Eolian deposition in the alpine zone of the Uinta Mountains, Utah, USA." CATENA 124 (January 2015): 119–29. http://dx.doi.org/10.1016/j.catena.2014.09.008.
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Webb, Casey, Michael Jensen, Bart Kowallis, Eric Christiansen, Douglas Sprinkel, and Sam Hudson. "Stratigraphic relationships of the Eocene Duchesne River Formation and Oligocene Bishop Conglomerate, northeastern Utah—pulsed sedimentary response to rollback of the subducted Farallon slab." Geology of the Intermountain West 9 (September 14, 2022): 153–79. http://dx.doi.org/10.31711/giw.v9.pp153-179.
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The Uinta Mountains are an east-west-trending, reverse fault-bounded, basement-cored Laramide uplift. The Eocene Duchesne River Formation and Oligocene Bishop Conglomerate represent late stage, intermontane basin fill of the Uinta Basin in northeastern Utah. Detailed mapping (1:24,000 scale), clast counts in conglomerate beds, description of lithology and stratigraphic contacts, and radiometric dating of pyroclastic fall beds of the Duchesne River Formation and Bishop Conglomerate in the Vernal NW quadrangle in northeastern Utah reveal stratal geometries of middle Cenozoic depositional units, the uplift and unroofing history of the eastern Uinta Mountains, and give evidence for the pulsed termination of Laramide uplift related to rollback of the Farallon slab and lithospheric delamination. These relationships show the continuation of Laramide uplift in this region until after 37.9 Ma and before 34 Ma, an age younger than the previously reported 45 to 40 Ma. The Duchesne River Formation consists of four members: the Brennan Basin, Dry Gulch Creek, Lapoint, and the Starr Flat. A normal unroofing signal is found within the formation with a downward increase in Paleozoic clasts and an upward increase in Proterozoic clasts. The oldest member, the Brennan Basin Member contains 80% to 90% Paleozoic clasts and less than 20% Proterozoic clasts. Conglomerate beds in the progressively younger Dry Gulch Creek, Lapoint, and Starr Flat Members of the Duchesne River Formation show significant increases in Proterozoic clasts (34% to 73%) and a decrease in Paleozoic clasts (27% to 66%). The Bishop Conglomerate overlies the Duchesne River Formation, but shows no clear change in clast composition. In the Duchesne River Formation, the proportion of beds containing fine gravel to boulder-sized clasts decreases significantly with distance from the Uinta uplift, from almost 100% near the source (<0.5 km) to 50% to 20% to the south (10 km). The lower part of the Duchesne River Formation exhibits a fining upward sequence that may represent a lull in tectonic uplift. The fine-grained lithofacies of the Dry Gulch Creek and Lapoint Members of the Duchesne River Formation pinch out within about 1 to 2 km from the Uinta uplift. In this proximal region conglomerates equivalent in age to the Lapoint Member cannot be separated from the younger conglomerates of the Starr Flat Member and are mapped together as one unit. Where the fine-grained lithologies appear farther from the uplift, the Starr Flat Member conglomerates deposited above Lapoint Member siltstones represent a southward progradation of alluvial fans away from the uplifting mountain front. The Starr Flat Member is overlain by the Bishop Conglomerate. These units are similar in sedimentary structure and clast composition and are distinguished by an angular unconformity that developed after 37.9 Ma. Stratigraphic and structural relationships between the Duchesne River Formation and Bishop Conglomerate reveal evidence of at least three episodes of Laramide-age uplift of the Uinta Mountains during the deposition of these formations: (1) deposition of fining upward sequences beginning with a basal coarse-grained unit within the Brennan Basin, Dry Gulch Creek, and Lapoint Members; (2) progradation of alluvial fans to the south form the younger Starr Flat Member resulted from an increase in sediment supply likely associated with renewed uplift; and (3) tilting and truncation of Duchesne River Formation to form the Gilbert Peak erosional surface, and prograding alluvial fans of the Bishop Conglomerate. These episodes of pulsed uplift are possibly the result of dripping lithosphere that occurred during Farallon slab rollback. New 40Ar/39Ar ages of 39.4 Ma from ash beds in the Dry Gulch Creek and Lapoint Members emplaced from Farallon rollback volcanism help to constrain the timing of deposition and uplift. These new ages and other existing radiometric and faunal ages suggest a significant unconformity of as much as 4 m.y. between the Duchesne River Formation and the overlying Bishop Conglomerate, which rangesfrom 34 to 30 Ma in age and show that Laramide uplift continued after 40 Ma in this region.
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Munroe, Jeffrey S., Ryan McElroy, Sam O'Keefe, Andrew Peters, and Luna Wasson. "Holocene records of eolian dust deposition from high‐elevation lakes in the Uinta Mountains, Utah, USA." Journal of Quaternary Science 36, no. 1 (September 22, 2020): 66–75. http://dx.doi.org/10.1002/jqs.3250.
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Carson, Eric C. "Hydrologic modeling of flood conveyance and impacts of historic overbank sedimentation on West Fork Black's Fork, Uinta Mountains, northeastern Utah, USA." Geomorphology 75, no. 3-4 (May 2006): 368–83. http://dx.doi.org/10.1016/j.geomorph.2005.07.022.
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Corbett, Lee B., and Jeffrey S. Munroe. "Investigating the influence of hydrogeomorphic setting on the response of lake sedimentation to climatic changes in the Uinta Mountains, Utah, USA." Journal of Paleolimnology 44, no. 1 (January 13, 2010): 311–25. http://dx.doi.org/10.1007/s10933-009-9405-9.
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Dalrymple, R. W., and G. M. Narbonne. "Continental slope sedimentation in the Sheepbed Formation (Neoproterozoic, Windermere Supergroup), Mackenzie Mountains, N.W.T." Canadian Journal of Earth Sciences 33, no. 6 (June 1, 1996): 848–62. http://dx.doi.org/10.1139/e96-064.
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The Sheepbed Formation (Ediacaran) is a 1 km thick, siliciclastic unit that overlies glacial deposits of the Ice Brook Formation and is overlain by carbonates of the Gametrail Formation. Observations in the Mackenzie Mountains indicate that the Sheepbed Formation accumulated in water depths of 1–1.5 km on a passive-margin, continental slope. The lower part of the formation consists predominately of dark mudstone. Fine-grained, turbiditic sandstone becomes more abundant upward, as does the scale and abundance of slope-instability indicators. Mesoscale facies successions (i.e., evidence of channels, lobes, and (or) compensation cycles) are developed in the upper half of the formation. The larger-scale changes are interpreted as reflecting a postglacial sea-level rise, followed by a relative fall and an increase in the rate of deposition. Contourites that may have been formed in response to the circulation of deep, cold water occur in the lowstand deposits. Their presence confirms previous speculation that the proto-Pacific Ocean was initiated at the beginning of Windermere deposition (ca. 780 Ma), not at the start of the Cambrian. The paleoflow direction toward the present-day northwest suggests that this part of Laurentia lay in the northern hemisphere. In situ Ediacaran megafossils are preserved on the soles of sandy turbidites; the deep-water setting indicates that these organisms were not photoautotrophs.
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Tabet, David. "Boron in the strata and waters of the Eocene Green River and Uinta Formations, Uinta Basin, Utah." Geosites 50 (September 1, 2022): 1–30. http://dx.doi.org/10.31711/ugap.v50i.111.
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Boron is a naturally occurring element that can be found in the strata and water of the Eocene Green River and Uinta Formations of the Uinta Basin of Utah. Whereas boron is suspected to be a necessary trace nutrient for proper plant and animal growth and development, higher concentrations of boron can be detrimental to living things, but the element is not known to be carcinogenic. Utah has no limit on boron content in drinking water; however, for irrigation purposes a limit of 750 μg B/L (0.75 mg/L) has been established. The Green River Formation (GRF), deposited in ancient lakes in Wyoming, Colorado, and Utah, is well known for its oil shale and saline mineral deposits, particularly the thick, economic trona beds in Wyoming. Such evaporitic mineral deposits are characteristic of a saline lake environment that existed at the end stages of Eocene lacustrine deposition. In Utah they are found in the upper GRF, and to a minor extent in the lower Uinta Formation, where elevated boron is evident. Boron-bearing minerals are present in the Parachute Creek Member of the GRF in Utah, and they occur as secondary silicate minerals in at least 12 wells across Utah’s Uinta Basin. These minerals were first reported by the U.S. Geological Survey in the 1950s. This study determined that the boron mineral occurrences correlate stratigraphically and coincide with the areas delineated for the hypersaline events in the Parachute Creek Member of the GRF. This argues that boron was concentrated with other saline constituents in Lake Uinta and is an indicator of hypersaline conditions. Water quality analyses reporting boron content from surface and subsurface samples were compiled from public databases from the Utah Department of Environmental Quality, the U.S. Geological Survey, and the Utah Geological Survey. This new database consists of 155 samples from 38 sites from the upper part (Parachute Creek Member) of the GRF, and 58 samples from 26 sites from the lower part (Douglas Creek Member) of the GRF. The boron concentration was found to be different for the two GRF parts. The average boron content of the 58 lower GRF aquifer water analyses is 6338 μg/L, while the mean boron content for the 26 individual sites varies from 15 to 205,000 μg/L. The upper GRF aquifer contains at least twice the boron content of the lower GRF, and the average boron content of the 155 analyses of upper GRF groundwater is 18,172 μg/L. The mean boron content for the 38 individual sites varies 40 to 480,000 μg/L. Areas of highboron concentration in groundwater of the GRF tend to coincide with the location of GRF hypersaline paleodepocenters. Groundwater boron content in the Uinta Formation comes from 40 analyses from 36 sites. The average of the 40 Uinta Formation analyses is 3251 μg B/L, while the mean boron content for the 36 individual sites varies from 40 to 24,000 μg/L. For each interval studied, less boron tends to be found in analyses from sites near the outcrop and boron content tends to increase in the studied formations as they are more deeply buried. Additionally, boron content was compiled for surface waters and springs for 3955 analyses from 374 sites in the Uinta Basin. When the mean boron content of these surface water sites was examined by hydrologic drainage unit subareas, it was found that the tributaries in the northern Uinta Basin, north of the Duchesne and White Rivers, contain the lowest mean boron contents, whereas higher mean boron contents are common for the tributaries in southern part of the basin. The boron content of surface water from the southern Uinta Basin drainages also tends to increase northward toward the demarking water courses. The tributaries in the southern part of the Uinta Basin have higher boron contents due to their waters having contact with the boron-bearing, shallow-inclined strata of the upper GRF or member B of the Uinta Formation. The tributaries in northern part of the basin have lower boron contents because they are not in contact with the GRF, have less contact with the member B of the Uinta Formation, and are diluted by greater snow-melt runoff from the Uinta Mountains which bound the basin to the north.
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Pisarska-Jamroży, Małgorzata, Katarzyna Machowiak, and Dariusz Krzyszkowski. "Sedimentation style of a Pleistocene kame terrace from the Western Sudety Mountains, S Poland." Geologos 16, no. 2 (June 1, 2010): 101–10. http://dx.doi.org/10.2478/v10118-009-0008-8.
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Sedimentation style of a Pleistocene kame terrace from the Western Sudety Mountains, S PolandThe depositional conditions of kame terraces in a mountain valley were analysed sedimentologically and petrologically through a series of kame terraces in the Rudawy Janowickie mountains. The kame terraces comprise five lithofacies associations. Lithofacies association GRt, Sp originates from deposition in the high-energy, deep gravel-bed channel of a braided river. Lithofacies association GC represents a washed out glacial till. Probably a thin layer of till was washed out by sandy braided rivers (Sp). The fourth association (Fh, Fm) indicates a shallow and quite small glaciomarginal lake. The last association (GRt, GRp) indicates the return of deposition in a sandy-bed braided channel. The petrography of the Janowice Wiekie pit and measurements of cross-stratified beds indicate a palaeocurrent direction from N to S. The Janowice Wielkie sedimentary succession accumulated most probably during the Saalian (Odranian, Saale I, Drenthe) as the first phase of ice-sheet melting, because the kame terrace under study is the highest one, 25-27 m above the Bóbr river level. The deposits under study are dominated by local components. The proglacial streams flowed along the margin of the ice sheet and deposited the kame terrace. The majority of the sedimentary succession was deposited in a confined braided-river system in quite deep channels.
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Clark, Peter U., Susan K. Short, Kerstin M. Williams, and John T. Andrews. "Late Quaternary chronology and environments of Square Lake, Torngat Mountains, Labrador." Canadian Journal of Earth Sciences 26, no. 10 (October 1, 1989): 2130–44. http://dx.doi.org/10.1139/e89-179.
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Sediment, pollen, and diatom records from Square Lake, a small lake dammed by a segment of Saglek Moraine, cover the period of deposition of and deglaciation from the Saglek Moraine. The basal radiocarbon date (18 210 ± 1900 years BP) is on sediment contaminated by reworked pollen and is thus a maximum age. However, the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the Saglek Moraine and thus establishes a Late Wisconsinan age for the Saglek Moraine. Vegetation on the ice-free upland surrounding Square Lake at this time was a sparse tundra vegetation dominated by grasses and herbs. The absence of diatoms indicates perennial lake-ice cover. A major transition is recorded by pollen and diatoms at > 8.5 ka. Vegetation probably remained sparse tundra, but birch and willow may have arrived in the area by 8 ka. Diatoms are first dominated by alkaliphil species, reflecting continued influence of glaciolacustrine sedimentation. An abrupt change in depositional environment ≥ 8 ka indicates ice retreat from the Saglek Moraine and start of nonglacial lacustrine sedimentation that has continued to the present. This was accompanied by an increase in organic matter, reflecting the newly established rich shrub tundra. At this time the diatoms also change, suggesting development of acidic organic soils around the lake. At 7.5 ka, diatoms indicate continued evolution of water chemistry and nutrient availability in the lake. Diatom concentrations and transfer function analyses of the pollen record identify the Holocene climatic optimum at 6.5 ka in the southern Torngat Mountains. The modern diatom flora was established at that time, but a decrease in diatom concentrations and estimated July temperatures suggest climatic deterioration in the area since 6.5 ka.
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MCLOUGHLIN, STEPHEN, and ANDREW N. DRINNAN. "Fluvial sedimentology and revised stratigraphy of the Triassic Flagstone Bench Formation, northern Prince Charles Mountains, East Antarctica." Geological Magazine 134, no. 6 (November 1997): 781–806. http://dx.doi.org/10.1017/s0016756897007528.
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The Flagstone Bench Formation ranges in age from earliest Triassic to Norian (Late Triassic) and is exposed in the Beaver Lake area of the northern Prince Charles Mountains. This sandstone-dominated formation rests conformably on the Bainmedart Coal Measures and represents the upper part of the Permian–Triassic Amery Group. It is divisible into three members: the Ritchie, Jetty and McKelvey members (in ascending order). Nine sedimentary facies assignable to three facies associations (major channel, crevasse/fan and flood-basin deposits) are recognized within the formation. Ritchie Member sedimentation took place during a transition from consistently hygric to seasonally dry conditions and the unit comprises sandstone-dominated, sheet-like channel deposits interspersed with few, thin, mottled, haematite-rich flood-basin siltstones. Deposition took place under fluctuating discharge conditions chiefly within the channel tracts of axially (northwesterly/northeasterly) flowing, low-sinuosity braided rivers. The Jetty Member shows a gross upward-fining profile dominated in the lower part by poorly sorted pebbly sandstones and in the upper part by ferruginous mudcracked siltstones, mottled palaeosols, calcrete and thin massive sandstone sheets. This unit reflects deposition of easterly directed alluvial fans and extensive flood-basin silt under a semi-arid climatic regime. The Upper Triassic sandstone-dominated McKelvey Member shows a return to axial drainage along the Lambert Graben with sedimentation occurring primarily within low-sinuosity braided channel tracts under wetter climatic conditions.
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Fujiki, Toshiyuki, Mitsuru Okuno, Toshio Nakamura, Shinji Nagaoka, Yuichi Mori, Kyoko Ueda, Masahiko Konomatsu, and Jun Aizawa. "AMS Radiocarbon Dating and Pollen Analysis of Core Ks0412-3 from Kashibaru Marsh in Northern Kyushu, Southwest Japan." Radiocarbon 55, no. 3 (2013): 1693–701. http://dx.doi.org/10.1017/s003382220004861x.
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We performed pollen analysis and accelerator mass spectrometry (AMS) radiocarbon dating on cored sediments (KS0412-3) from Kashibaru Marsh, located in the western part of the Sefuri Mountains in northern Kyushu, southwestern Japan, to investigate environmental change around the marsh. Sediment accumulation began in this marsh around cal AD 1200 and continued with an estimated average sedimentation rate of about 4 mm/yr. Human rice cultivation at this location began around cal AD 1300 and was abandoned due to the deposition of a thick sand layer at around cal AD 1400. Since this event, the area has been maintained as a “natural” marsh.
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Kováč, Michal, Jozef Hók, Jozef Minár, Rastislav Vojtko, Miroslav Bielik, Radovan Pipík, Miloš Rakús, Ján Kráľ, Martin Šujan, and Silvia Králiková. "Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance model." Geologica Carpathica 62, no. 4 (August 1, 2011): 361–79. http://dx.doi.org/10.2478/v10096-011-0027-6.
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Neogene and Quaternary development of the Turiec Basin and landscape in its catchment: a tentative mass balance modelThe development of the Turiec Basin and landscape evolution in its catchment has been reconstructed by methods of geological research (structural geology, sedimentology, paleoecology, and geochronological data) as well as by geophysics and geomorphology. The basin and its surrounding mountains were a subject of a mass balance study during periods of tectonic activity, accompanied by considerable altitudinal differentiation of relief and also during quiet periods, characterized by a development of planation surfaces in the mountains. The coarse clastic alluvial fans deposited beneath the offshore pelitic sediments document the rapid Middle Miocene uplift of mountains on the margin of the Turiec Basin. The Late Miocene finegrained sedimentation represents the main fill of this basin and its origin was associated with the formation of planation surfaces in the surrounding mountains. The rapid uplift of the western and northern parts of the catchment area during the latest Miocene and Early Pliocene times further generated the deposition of coarse-grained alluvial fans. The Late Pliocene basin inversion, due to uplift of the whole Western Carpathians mountain chain, was associated with the formation of the Early Quaternary pediment and ultimately with the formation of the Turiec river terrace systems.
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MARYNOWSKI, LESZEK, PAWEŁ FILIPIAK, and MICHAŁ ZATOŃ. "Geochemical and palynological study of the Upper Famennian Dasberg event horizon from the Holy Cross Mountains (central Poland)." Geological Magazine 147, no. 4 (January 15, 2010): 527–50. http://dx.doi.org/10.1017/s0016756809990835.
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AbstractIntegrated palynological, organic and inorganic geochemical and petrographical methods have been used for deciphering the depositional redox conditions and character of organic matter of the Famennian Dasberg event horizon from the deep-shelf Kowala succession of the Holy Cross Mountains. The ages of the investigated samples have been established, using miospore data, as VF (Diducites versabilis–Grandispora famenensis) and LV (Retispora lepidophyta–Apiculiretusispora verrucosa) miospore Zones of the Middle/Upper Famennian. In the standard conodont zonation, this corresponds to the uppermost postera to lowermost praesulcata Zones. The presence of green sulphur bacteria biomarkers and dominance of small-sized framboids together with the presence of large framboids and low values of the U/Th ratio may indicate that during sedimentation of the lower Dasberg shale, intermittent anoxia occurred in the water column, or the anoxic conditions prevailed in the upper part of the water column, while the bottom waters were oxygenated, at least briefly. Deposition of the upper Dasberg shale was characterized by both bottom water and water column anoxia. The lack of acritarcha taxa from these intervals could have been due to anoxia in the photic zone. Moreover, organic content is high in those samples. There is no geochemical evidence for anoxia during sedimentation of the deposits sandwiched between the lower and upper Dasberg shales, or in the deposits which underlie and overlie both Dasberg shale horizons. The two discrete anoxic events are interpreted to be the result of major transgressions and the blooming of primary producers. Above the Dasberg shales, small fragments of charcoal and raised concentrations of polycyclic aromatic hydrocarbons are detected. This supports the presence of wildfires during deposition of shales just above the boundary of VF/LV palynological zones. Temperatures calculated from the fusinite reflectance values suggest that the charcoal was formed in low-temperature ground and/or surface fires. The typical marine character of sedimentation combined with the high proportion of charcoals suggests that wildfires were large-scale, and that there was intensive transport of terrestrial material. The main causes of intensive wildfires were a significant rise of O2 in the atmosphere and important progress in the land plant diversity during Late Devonian times. Palynofacies studies suggest that the transgression corresponds to the part IIf of the Late Devonian sea-level curve.
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Cook, Y. A. "Precambrian rift-related magmatism and sedimentation, south Victoria Land, Antarctica." Antarctic Science 19, no. 4 (August 16, 2007): 471–84. http://dx.doi.org/10.1017/s0954102007000612.
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AbstractPrecambrian continental extension is described in detail for the first time in the Victoria Land segment of the Transantarctic Mountains and is comparable with plume related intercontinental rifting of the Afar area, Africa. The Baronick Formation comprises igneous-derived conglomerate, marble and volcanic to sub-volcanic igneous layers. Volcanic and carbonate horizons were eroded in a fluvial or marine environment and provided debris for mass flow and slump deposits which formed in a marginal marine basin in the Precambrian. Clasts in these deposits include basalt, trachyte and comendite, and along with the interbedded volcanic layers of basalt, trachyte and quartz syenite, indicate proximity and contemporaneity of volcanic activity. Igneous layers and source rocks for clasts of the Baronick Formation have an enriched MORB chemistry and underwent albitization of calcic feldspar before erosion and conglomerate deposition. The Highway Suite forms a kilometre-scale body of gabbro and dolerite plugs and is interpreted as a slice of transitional continental oceanic crust. The chemistry of all igneous rocks suggests a continental rift environment and the associated sediments are consistent with such a setting. The Baronick Formation was locally intruded by sills of the Highway Suite; however, the main body of the Highway Suite was juxtaposed against the Baronick Formation during greenschist facies shearing before c. 551 Ma.
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Evans, David JA, Keith E. Salt, and Claire S. Allen. "Glacitectonized lake sediments, Barrier Lake, Kananaskis Country, Canadian Rocky Mountains." Canadian Journal of Earth Sciences 36, no. 3 (March 25, 1999): 395–407. http://dx.doi.org/10.1139/e98-093.
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Stratigraphic and sedimentological analyses of exposures through a glacilacustrine sedimentary sequence along the south shore of Barrier Lake, Kananaskis Country, reveal evidence of glacitectonic disturbance, relating to a readvance of the Bow Valley glacier at the end of the last glaciation. Prior to disturbance, palaeocurrent measurements in gravel and sand foreset beds record the deposition of subaqueous fans-deltas from a glacier lobe retreating eastwards along the Barrier Lake depression. The fan-delta sediments fine upwards into ripple- and cross-bedded sands and laminated muds with dropstones, documenting progressively distal sedimentation. Palaeostress directions measured from large-scale folds, shear zones and glacitectonites, and deformation tills indicate that glacier ice readvanced southwards from a glacier lobe located over the Barrier Lake depression. These stress directions are used to reconstruct the flow lines within the southern margin of a low-profile glacier lobe that terminated halfway up lower Barrier Lake, a more extensive readvance than previously envisaged in the area for this period. Comparisons of diamicton and glacitectonite fabric shapes with similar sediments elsewhere indicate that the subglacially deformed material that caps some of the sections is immature and has undergone short travel distances. Although the exact age of the readvance is unknown, it probably represents the Canmore Readvance of the Late Wisconsinan glaciation.
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SMOLAREK, JUSTYNA, WIESŁAW TRELA, DAVID P. G. BOND, and LESZEK MARYNOWSKI. "Lower Wenlock black shales in the northern Holy Cross Mountains, Poland: sedimentary and geochemical controls on the Ireviken Event in a deep marine setting." Geological Magazine 154, no. 2 (February 4, 2016): 247–64. http://dx.doi.org/10.1017/s0016756815001065.
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AbstractThe stratigraphic variability and geochemistry of Llandovery/Wenlock (L/W) Series boundary sediments in Poland reveals that hemipelagic sedimentation under an anoxic/euxinic water column was interrupted by low-density bottom currents or detached diluted turbid layers that resulted in intermittent seafloor oxygenation. Total organic carbon values and inorganic proxies throughout the Wilków 1 borehole section suggest variable redox conditions. U/Mo ratios > 1 throughout much of the Aeronian and Telychian stages, together with an absence of pyrite framboids, suggest oxygenated conditions prevailed. However, elevated total organic carbon near the Aeronian/Telychian boundary, together with increased U/Th and V/(V + Ni) ratios and populations of small pyrite framboids are consistent with the development of dysoxic/anoxic conditions at that time. U/Th, V/Cr and V/(V + Ni) ratios, as well as Uauthig and Mo concentrations, suggest that during the Ireviken black shale deposition, bottom-water conditions deteriorated from oxic during Telychian time to mostly suboxic/anoxic immediately prior to the L/W boundary, before a brief reoxygenation at the end of the Ireviken black shale sedimentation in the Sheinwoodian Stage. Rapid fluctuations in U/Mo during the Ireviken Event are characteristic of fluctuating redox conditions that culminated in an anoxic/euxinic seafloor in Sheinwoodian time. Following Ireviken black shale deposition, conditions once again became oxygen deficient with the development of a euxinic zone in the water column. The Aeronian to Sheinwoodian deep-water redox history was unstable, and rapid fluctuations of the chemocline across the L/W Series boundary probably contributed to the Ireviken Event extinctions, which affected mainly pelagic and hemipelagic fauna.
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Trop, Jeffrey M., Kenneth D. Ridgway, Arthur R. Sweet, and Paul W. Layer. "Submarine fan deposystems and tectonics of a Late Cretaceous forearc basin along an accretionary convergent plate boundary, MacColl Ridge Formation, Wrangell Mountains, Alaska." Canadian Journal of Earth Sciences 36, no. 3 (March 25, 1999): 433–58. http://dx.doi.org/10.1139/e98-103.
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Analysis of Upper Cretaceous sedimentary and volcanic strata in the Wrangell Mountains of south-central Alaska provides an opportunity to study the tectonics, depositional systems, and provenance of a forearc basin that developed along an accretionary convergent plate boundary. New data from the 1150 m thick MacColl Ridge Formation indicate that deposition occurred during the Campanian on a coarse-grained submarine fan that was derived from an uplifted allochthonous terrane exposed in the hanging wall of a fault system that separated the forearc basin from the subduction complex. New age controls include palynoflora indicative of a late middle to late Campanian age, and compatible radiometric age determinations of volcanic vitric-crystal tuffs near the top of the formation which have 40Ar/39Ar isochron ages of 79.4 ± 0.7 and 77.9 ± 2.1 Ma. Sedimentological and paleontological data show that sedimentation occurred on the inner portions of a sand- and gravel-rich submarine fan system. Evidence for this interpretation includes dominance of channelized sediment gravity flow deposits, particularly turbidites and debris flows; microflora indicative of open-marine conditions; unidirectional paleocurrent indicators; and syndepositional slump features. The pyroclastic eruptions that formed the vitric-crystal tuffs of the MacColl Ridge Formation are interpreted as products of the Late Cretaceous Kluane magmatic arc that bordered the forearc basin to the north. Sandstone and conglomerate compositional data combined with northward-directed paleocurrent indicators suggest that detritus was derived mainly from igneous rocks of the allochthonous Wrangellia terrane located in the hanging wall of the Border Ranges fault system along the southern margin of the basin. From a regional perspective, deposition of the MacColl Ridge Formation was coeval with the early part of Campanian-Maastrichtian synorogenic sedimentation and contractile deformation documented throughout the northwestern Cordillera.
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Devlin, William J. "Stratigraphy and sedimentology of the Hamill Group in the northern Selkirk Mountains, British Columbia: evidence for latest Proterozoic – Early Cambrian extensional tectonism." Canadian Journal of Earth Sciences 26, no. 3 (March 1, 1989): 515–33. http://dx.doi.org/10.1139/e89-044.
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Three informal stratigraphic divisions are recognized in the uppermost Proterozoic – Lower Cambrian Hamill Group in the northern Selkirk Mountains of British Columbia. These informal divisions include a lower sandstone unit, a greenstone–graded-sandstone unit, and an upper sandstone unit. Both the lower and upper sandstone units display sedimentary characteristics that are uniform along strike and indicate a shallow-marine environment of deposition. As is typical of other exposures of the Hamil Group in southeastern British Columbia, the lower sandstone unit is coarser grained and more poorly sorted than the mature quartz arenites of the upper sandstone unit.The greenstone–graded-sandstone unit is a complex assemblage of mafic metavolcanic rocks and associated sandstone facies. This unit is highly variable along strike but essentially consists of a thick succession of subaqueous extrusive rocks overlain by a variety of sediment gravity-flow deposits. These latter deposits include resedimented conglomerates, debris-flow deposits, and trubidites (deposited from both high- and low-density turbidity currents). Stratigraphic sections of this unit are described in detail from three different localities and are examined in terms of their transport and depositional mechanisms.The stratigraphic succession of the Hamill Group indicates that deposition of the shallow-marine sands of the lower sandstone unit was abruptly interrupted by a period of volcanism, the creation of a paleoslope, and the deposition of a large volume of sediment gravity-flow deposits of the greenstone–graded-sandstone unit. These relations are attributed to an episode of syndepositional normal faulting. The inferred fault(s) could have served as the conduit for the extrusion of the volcanics. Offset along the fault(s), the tilting of fault blocks, and the consequent formation of an unstable slope adjacent to a fault scarp created an environment favorable for deposition of the sediment gravity flows. In general, deposition of proximal, base-of-slope deposits was followed by an aggradational basin-fill phase of sedimentation. With the waning of tectonic activity and the filling of the fault-bounded basin, depositon of shallow-marine sands resumed (the upper sandstone unit). The stratigraphic relations of the Hamill Group in the northern Selkirk Mountains are considered direct evidence for an episode of latest Proterozoic – Early Cambrian extensional tectonism. The evidence for an episode of rift-related tectonism in the northern Selkirk Mountains supports inferences concerning the timing of this event as derived from tectonic subsidence analyses of post-rift strata of the Cordilleran miogeocline.
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Elias, Robert J., Danita S. Brandt, and T. H. Clark. "Late Ordovician solitary rugose corals of the St. Lawrence Lowland, Québec." Journal of Paleontology 64, no. 3 (May 1990): 340–52. http://dx.doi.org/10.1017/s0022336000018540.
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Two species of solitary rugose corals occur in Late Ordovician strata of the St. Lawrence Lowland. Grewingkia canadensis (Billings, 1862) appears in the upper part of the Nicolet River Formation (upper St. Hilaire Member) and is far more common in the overlying Pontgravé River Formation. A single specimen of Streptelasma divaricans (Nicholson, 1875) is known from the Pontgravé River. Their presence confirms that this area is situated within the Richmond Province and that the upper Nicolet River, as well as the Pontgravé River, is Richmondian in age. Solitary Rugosa were introduced to this biogeographic province during an early Richmondian transgression, marked in the upper Nicolet River Formation by a coarser clastic interval. That event permits correlation between the St. Lawrence Lowland in the eastern part of the Richmond Province and the North American type Upper Ordovician (Cincinnatian Series) of the Cincinnati Arch region in the western part of the province.A comparative morphologic, paleoecologic, and biostratinomic analysis of solitary corals indicates that normal, low-energy conditions were interrupted occasionally by high-energy events (probably storms) during deposition of the upper Nicolet River and Pontgravé River Formations. Water depth increased northwestward in the St. Lawrence Lowland area. Deposition of these siliciclastic prodelta to delta front sediments was generally continuous and the sedimentation rate was usually high because of rapid basin subsidence and comparatively close proximity to the Taconic Mountains. In the western part of the Richmond Province, farther from the source area, carbonate as well as clastic sediments accumulated, periods of nondeposition were more frequent, and the sedimentation rate was relatively low. Corals disappeared from the St. Lawrence Lowland area during the Richmondian, when delta top facies of the Bécancour River Formation succeeded the Pontgravé River Formation due to a glacio-eustatic regression and progradation of the Queenston Delta.
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Vierek, Aleksandra. "Source and depositional processes of coarse-grained limestone event beds in Frasnian slope deposits (Kostomłoty-Mogiłki quarry, Holy Cross Mountains, Poland)." Geologos 16, no. 3 (October 14, 2010): 153–68. http://dx.doi.org/10.2478/v10118-009-0010-1.
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Source and depositional processes of coarse-grained limestone event beds in Frasnian slope deposits (Kostomłoty-Mogiłki quarry, Holy Cross Mountains, Poland)The Kostomłoty-Mogiłki succession is situated in the Kostomłoty transitional zone between the shallow-water Kielce stromatoporoid-coral platform and the deeper Łysogóry basin. In the Kostomłoty-Mogiłki quarry, the upper part of the Szydłówek Beds and Kostomłoty Beds are exposed. The Middle-Upper Frasnian Kostomłoty Beds are composed of shales, micritic and nodular limestones with abundant intercalations of detrital limestones. The dark shales and the micritic and nodular limestones record background sedimentation. The interbedded laminated and detrital limestones reflect high-energy deposition (= event beds). These event beds comprise laminated calcisiltites, fine-grained calcarenites, coarse-grained grain-supported calcirudites fabrics, and matrix-supported calcirudites. The material of these event beds was supplied by both erosion of the carbonate-platform margin and cannibalistic erosion of penecontemporaneous detrital limestones building the slope of this platform. Storms and the tectonic activity were likely the main causes of erosion. Combined and gravity flows were the transporting mechanisms involved in the reworking and redeposition.
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Soto-Kerans, Graham M., Daniel F. Stockli, Xavier Janson, Timothy F. Lawton, and Jacob A. Covault. "Orogen proximal sedimentation in the Permian foreland basin." Geosphere 16, no. 2 (January 6, 2020): 567–93. http://dx.doi.org/10.1130/ges02108.1.
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Abstract The sedimentary fill of peripheral foreland basins has the potential to preserve a record of the processes of ocean closure and continental collision, as well as the long-term (i.e., 107–108 yr) sediment-routing evolution associated with these processes; however, the detrital record of these deep-time tectonic processes and the sedimentary response have rarely been documented during the final stages of supercontinent assembly. The stratigraphy within the southern margin of the Delaware Basin and Marathon fold and thrust belt preserves a record of the Carboniferous–Permian Pangean continental assembly, culminating in the formation of the Delaware and Midland foreland basins of North America. Here, we use 1721 new detrital zircon (DZ) U-Pb ages from 13 stratigraphic samples within the Marathon fold and thrust belt and Glass Mountains of West Texas in order to evaluate the provenance and sediment-routing evolution of the southern, orogen-proximal region of this foreland basin system. Among these new DZ data, 85 core-rim age relationships record multi-stage crystallization related to magmatic or metamorphic events in sediment source areas, further constraining source terranes and sediment routing. Within samples, a lack of Neoproterozoic–Cambrian zircon grains in the pre-orogenic Mississippian Tesnus Formation and subsequent appearance of this zircon age group in the syn-orogenic Pennsylvanian Haymond Formation point toward initial basin inversion and the uplift and exhumation of volcanic units related to Rodinian rifting. Moreover, an upsection decrease in Grenvillian (ca. 1300–920 Ma) and an increase in Paleozoic zircons denote a progressive provenance shift from that of dominantly orogenic highland sources to that of sediment sources deeper in the Gondwanan hinterland during tectonic stabilization. Detrital zircon core-rim age relationships of ca. 1770 Ma cores with ca. 600–300 Ma rims indicate Amazonian cores with peri-Gondwanan or Pan-African rims, Grenvillian cores with ca. 580 Ma rims are correlative with Pan-African volcanism or the ca. 780–560 Ma volcanics along the rifted Laurentian margin, and Paleozoic core-rim age relationships are likely indicative of volcanic arc activity within peri-Gondwana, Coahuila, or Oaxaquia. Our results suggest dominant sediment delivery to the Marathon region from the nearby southern orogenic highland; less sediment was delivered from the axial portion of the Ouachita or Appalachian regions suggesting that this area of the basin was not affected by a transcontinental drainage. The provenance evolution of sediment provides insights into how continental collision directs the dispersal and deposition of sediment in the Permian Basin and analogous foreland basins.
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MARYNOWSKI, LESZEK, and PAWEŁ FILIPIAK. "Water column euxinia and wildfire evidence during deposition of the Upper Famennian Hangenberg event horizon from the Holy Cross Mountains (central Poland)." Geological Magazine 144, no. 3 (April 16, 2007): 569–95. http://dx.doi.org/10.1017/s0016756807003317.
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A palynological study of the uppermost Famennian section from Kowala Quarry (Holy Cross Mountains, central Poland) allowed recognition of two miospore zones: LV (Retispora lepidophyta–Apiculiretusispora verrucosa) and LN (Retispora lepidophyta–Verrucosisporites nitidus). Based on palynology and sedimentology, the black shale within the upper part of the section is identified as equivalent to the Hangenberg Black Shale, which is known globally. This black shale contains compounds characteristic of photic zone euxinia, including isorenieratane and its derivatives. Such compounds are absent in the organic-poor marls and shales occurring below the LN Zone, and are present only as traces in the layers just above the black shale, indicating fluctuations in the oxygen minimum zone during uppermost Famennian sedimentation. Palynofacies show high amounts of amorphous organic matter and prasinophyte concentrations in the black shale, and a subsequent significant decrease of amorphous organic matter concomitant with a rapid increase of terrestrial input (mainly miospores with common tetrads) in the layers above the black shale. This supports the relatively rapid change in the taxonomic composition of phytoplankton caused by fluctuations of the chemocline. The whole succession corresponds to one sea-level rise and fall. The presence of high concentrations of peri-condensed polycyclic aromatic hydrocarbons and large amounts of small charcoal particles at the Hangenberg event horizon indicate the occurrence of wildfires. Such observations suggest that atmospheric O22 levels had exceeded the critical threshold of 13 %, above which wildfires may occur, by latest Famennian time.
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Sztanó, Orsolya, Krisztina Sebe, Gábor Csillag, and Imre Magyar. "Turbidites as indicators of paleotopography, Upper Miocene Lake Pannon, Western Mecsek Mountains (Hungary)." Geologica Carpathica 66, no. 4 (August 1, 2015): 331–44. http://dx.doi.org/10.1515/geoca-2015-0029.
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AbstractThe floor of Lake Pannon covering the Pannonian Basin in the Late Miocene had considerable relief, including both deep sub-basins, like the Drava Basin, and basement highs, like the Mecsek Mts, in close proximity. The several km thick lacustrine succession in the Drava Basin includes profundal marls, basin-center turbidites, overlain by shales of basin-margin slopes, coarsening-upward deltaic successions and alluvial deposits. Along the margin of the Mecsek Mts locally derived shoreface sands and deltaic deposits from further away have been mapped so far on the surface. Recent field studies at the transition between the two areas revealed a succession that does not fit into either of these environments. A series of sandstone a few meters thick occurs above laminated to bioturbated clayey siltstone. The sandstone show normal grading, plane lamination, flat erosional surfaces, soft-sediment deformations (load and water-escape structures) and sharp-based beds with small reverse faults and folds. These indicate rapid deposition from turbidity currents and their deformation as slumps on an inclined surface. These beds are far too thick and may reveal much larger volumes of mass wasting than is expected on the 20–30 m high delta slopes; however, regional seismic lines also exclude outcropping of deep-basin turbidites. We suggest that slopes with transitional size (less than 100 m high) may have developed on the flank of the Mecsek as a consequence of lake-level rise. Although these slopes were smaller than the usually several hundred meter high clinoforms in the deep basins, they could still provide large enough inertia for gravity flows. This interpretation is supported by the occurrence of sublittoral mollusc assemblages in the vicinity, indicating several tens of meters of water depth. Fossils suggest that sedimentation in this area started about 8 Ma ago.
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Herkat, Missoum. "Eustatic and palaeogeographic control of the western Aurès Upper Cretaceous sedimentation (Algeria)." Bulletin de la Société Géologique de France 175, no. 3 (May 1, 2004): 273–88. http://dx.doi.org/10.2113/175.3.273.
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Abstract The Upper Cretaceous sedimentation in the Aurès Mountains occurred in a subsident basin delimited to the south by the Saharan platform and by the Preatlasic high zone to the north. In these series 4 transgressive-regressive megasequences are distinguished, the first one (I) in the late Albian-Cenomanian, the second one (II) in the Turonian, the third one (III) in the Coniacian - Santonian and the fourth one (IV) in the Campanian - Maastrichtian. Each megasequence is made up of three or four sequences, which correspond to third order cycles identified in the eustatic chart of Haq et al. [1987]. In late Albian and lower Turonian periods, during the deposition of basal sequences of the megasequences I and II, the reactivation of basement faults in the Aurès basin occurs consecutively to distension phases, resulting in the formation of rotated blocks. At the same time high eustatic levels are reached according to the global eustatic curve. These processes control the drowning of the carbonate platforms pre-existing to these sequences, and deep ramps progressively form on the tilted block tops. This sedimentary setting generates in the late Albian and lower Turonian series anoxic sequences made up of calcareous and shaly transgressive pelagic intervals. The succeeding sequences lack pelagic facies and are composed of alternate marls / carbonate beds deposited on a homoclinal ramp, indicating a gradual development of shallow open marine conditions, which became progressively restricted upwards. Toward the top of these megasequences, lagunal muds and isolated rudists mounds, surrounded by bioclastic and ooid / pellet banks occur. The Coniacian-Santonian and Campanian-Maastrichtian megasequences are characterized by a shallow ramp sedimentation, essentially marly during the Coniacian, Santonian and Campanian periods, interlayered with some bioclastic / ooid carbonate banks and upwards by sequences mostly homogeneous. The Maastrichtian platform carbonates are composed of bioclastic / ooid sands and were deposited in a ramp-barrier-bank system. Some sequences in the Campanian-Maastrichtian megasequence are condensed or absent due to the accommodation reduction related to a weak subsidence rate period.
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Kaufman, Darrell S., Steven L. Forman, Peter D. Lea, and Cameron W. Wobus. "Age of Pre-late-Wisconsin Glacial-Estuarine Sedimentation, Bristol Bay, Alaska." Quaternary Research 45, no. 1 (January 1996): 59–72. http://dx.doi.org/10.1006/qres.1996.0006.
Full textAbstract:
AbstractPleistocene glacial-estuarine sediment deposited in an intertidal environment of northeastern Bristol Bay, southwestern Alaska, was dated using a variety of approaches, including infrared stimulated and thermoluminescence (IRSL and TL) techniques. Analysis of modern and 14C-dated Holocene tide-flat mud demonstrates that the bulk of sediment in this environment is reset by solar radiation, thereby lending confidence to ages obtained from similar Pleistocene deposits by luminescence techniques. IRSL seems to be especially well suited for dating, with resolution on time scales of <10,000 yr. The ages of tide-flat mud of the Nushagak Formation, derived from the Ahklun Mountains to the northwest of Bristol Bay, and of Halfmoon Bay drift, derived from the Alaska Peninsula to the southeast, suggest contemporaneous glacial-estuarine deposition related to independent glacial source areas about 75,000–80,000 yr ago. This age is consistent with other geochronological data that indicate a pre-late-Wisconsin and post-substage-5e age, including nonfinite 14C ages, a lack of interglacial indicators, and Old Crow tephra (∼140,000 yr) atop the drift, normal paleomagnetic inclinations, and amino acid (isoleucine) epimerization ratios (aIle/Ile). AIle/Ile ratios in Portlandia arctica(0.052 ± 0.003) from a marine-lag horizon at South Naknek beach, which separates Halfmoon Bay drift above from older glacial-estuarine drift below, are only slightly higher than in Mya truncata(0.041 ± 0.007) from last-interglacial Pelukian deposits at Nome. As laboratory heating experiments show that the two genera epimerize at similar rates, these data imply correlation of the marine lag at South Naknek beach with Pelukian deposits. Hence, glaciers on the Alaska Peninsula experienced major pre-late-Wisconsin advances both before and after the last interglaciation. Shells reworked into Halfmoon Bay drift yield aIle/Ile ratios of 0.028 ± 0.005 for Portlandiaat Second Point and 0.027 ± 0.001 for Hiatella arcticaat Etolin Point. Together with assumptions about the postdepositional temperature history, these ratios indicate that the shells are at least 55,000 yr, and probably closer to ∼90,000 yr, although the uncertainty in this age estimate is broad. The amino acid and luminescence data converge on an age between about 75,000, and 90,000 yr, late during oxygen-isotope stage 5, for a major ice advance far beyond late-Wisconsin limits.
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Cook, Frederick A., John L. Varsek, and Elizabeth A. Clark. "Proterozoic craton to basin crustal transition in western Canada and its influence on the evolution of the Cordillera." Canadian Journal of Earth Sciences 28, no. 8 (August 1, 1991): 1148–58. http://dx.doi.org/10.1139/e91-105.
Full textAbstract:
Deep seismic reflection data have imaged a crustal-scale, west-facing ramp or ramp system in the subsurface of western Canada. In northwestern Canada the ramp is within Proterozoic crust east of the Cordillera and is unconformably overlain by Paleozoic sedimentary rocks, indicating that it was formed during the Proterozoic in this region. Similar structures are visible within the Cordillera in southern Canada and the northwestern United States along a south projection of the ramp observed in the north. In the Monashee Complex of British Columbia and in the Priest River Complex in northern Washington, reflections are visible that dip westward from the surface to near the base of the crust and are structurally discordant with underlying more horizontal reflections, thus outlining footwall ramps. We propose that the Proterozoic crustal ramp in the north and the footwall ramps in the Cordillera probably coincide with a Proterozoic crustal transition from thick craton on the east to thin crust on the west. This transition may have influenced sedimentation patterns during deposition of Middle Proterozoic Belt–Purcell and Wernecke strata (ca. 1.6–1.3 Ga) and probably controlled the arcuate shape of the Mackenzie Mountains during their formation in the Mesozoic. This interpretation is consistent with the notion that thrust sheets of the Mackenzie Mountains did not extend onto the craton a sufficient distance to produce flexural subsidence of the thick crust and associated foreland basin development, whereas thrust sheets of the southern Canadian Cordillera were driven eastward and loaded the thick craton, causing crustal flexure and development of the Alberta Basin.
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Caylor, Emilia A., Barbara Carrapa, Kurt Sundell, Peter G. DeCelles, and Joshua M. Smith. "Age and deposition of the Fort Crittenden Formation: A window into Late Cretaceous Laramide and Cenozoic tectonics in southeastern Arizona." GSA Bulletin 133, no. 9-10 (January 27, 2021): 1996–2016. http://dx.doi.org/10.1130/b35808.1.
Full textAbstract:
Abstract The Upper Cretaceous Fort Crittenden Formation exposed in the Santa Rita and Huachuca Mountains of southeastern Arizona is a syntectonic deposit that has been associated with Laramide tectonic activity. However, the spatio-temporal relationships among Cretaceous sedimentation, magmatism, basement exhumation, and possible flat slab-related processes in the southern Laramide region remain poorly understood. Age controls for uplift and erosion of local topography and syntectonic deposition in response to deformation remain particularly poor. The Fort Crittenden Formation comprises 800–2500 m of locally derived fluvial to alluvial fan sedimentary rocks and records paleodrainage reorganization in response to active tectonics. Changes in sedimentary facies, provenance, and paleoflow suggest deposition in a tectonically partitioned intraforeland basin. New detrital zircon data constrain the timing of deposition of the Fort Crittenden Formation between ca. 86 Ma and ca. 76 Ma. The lack of depositional age zircons throughout the majority of the Fort Crittenden Formation is consistent with a magmatic lull in the Cordilleran arc between ca. 90 Ma and ca. 76 Ma. The overlying Salero Formation and Late Cretaceous intrusions are expressions of renewed magmatism in southeastern Arizona at ca. 75 Ma. New Lu-Hf data indicate that magmas evolved from contamination of old juvenile crust. When interpreted in conjunction with other regional data sets, our study indicates that the Laramide deformation front migrated eastward into southwestern New Mexico by 75 Ma. Thermal modeling of apatite fission track and (U-Th)/He data from granitic clasts are consistent with Late Cretaceous–Paleocene (ca. 76–55 Ma) heating related to magmatism and cooling and exhumation during the Eocene and Oligocene.
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Helmens, Karin F., Rene W. Barendregt, Randolph J. Enkin, Judith Baker, and Paul A. M. Andriessen. "Magnetic Polarity and Fission-Track Chronology of a Late Pliocene–Pleistocene Paleoclimatic Proxy Record in the Tropical Andes." Quaternary Research 48, no. 1 (July 1997): 15–28. http://dx.doi.org/10.1006/qres.1997.1886.
Full textAbstract:
Two sections exposing a Late Pliocene–Pleistocene sedimentary sequence in the marginal valleys of the Bogotá Basin (Colombian Andes, South America) were sampled for paleomagnetic analysis. Magnetostratigraphy and fission-track dates of tephra beds provide a detailed geochronologic calibration for the sedimentary basin. Measurements of magnetic susceptibility complement the regional environmental record provided by lithological and palynological evidence. Sedimentation in the Bogota Basin started in the early part of the Gauss Chron at ca. 3.2 myr. The oldest recorded sediments belong to the Guasca Member of the Upper Tilatá Formation. They were deposited in a lacustrine/paludal environment, near the end of the tectonic uplift in the Bogotá area, and/or under Pliocene climatic conditions that were warmer than today. Repeated climate cooling associated with glaciations in the surrounding mountains resulted in the deposition of a fluvial–lacustrine complex referred to as the Subachoque Formation. The first glaciation is placed near the Gauss/Matuyama polarity reversal at 2.6 myr. A lithologic change in the Subachoque Formation marked by coarser-grained fluvial deposits and a possible increase in amplitude of the magnetic susceptibility signal occurs near the Matuyama/Brunhes boundary at 0.8 myr, indicating a shift toward higher magnitude climate oscillations.
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Villagómez Díaz, Diego, Silvia Omodeo-Salé, Alexey Ulyanov, and Andrea Moscariello. "Insights into the Thermal History of North-Eastern Switzerland—Apatite Fission Track Dating of Deep Drill Core Samples from the Swiss Jura Mountains and the Swiss Molasse Basin." Geosciences 11, no. 1 (December 27, 2020): 10. http://dx.doi.org/10.3390/geosciences11010010.
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This work presents new apatite fission track LA–ICP–MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) data from Mid–Late Paleozoic rocks, which form the substratum of the Swiss Jura mountains (the Tabular Jura and the Jura fold-and-thrust belt) and the northern margin of the Swiss Molasse Basin. Samples were collected from cores of deep boreholes drilled in North Switzerland in the 1980s, which reached the crystalline basement. Our thermochronological data show that the region experienced a multi-cycle history of heating and cooling that we ascribe to burial and exhumation, respectively. Sedimentation in the Swiss Jura Mountains occurred continuously from Early Triassic to Early Cretaceous, leading to the deposition of maximum 2 km of sediments. Subsequently, less than 1 km of Lower Cretaceous and Upper Jurassic sediments were slowly eroded during the Late Cretaceous, plausibly as a consequence of the northward migration of the forebulge of the neo-forming North Alpine Foreland Basin. Following this event, the whole region remained relatively stable throughout the Paleogene. Our data show that the Tabular Jura region resumed exhumation at low rates in early–middle Miocene times (≈20–15 Ma), whereas exhumation in the Jura fold-and-thrust belt probably re-started later, in the late Miocene (≈10–5 Ma). Erosional exhumation likely continues to the present day. Despite sampling limitations, our thermochronological data record discrete periods of slow cooling (rates of about 1°C/My), which might preclude models of elevated cooling (due to intense erosion) in the Jura Mountains during the Miocene. The denudation (≈1 km) of the Tabular Jura region and the Jura fold-and-thrust belt (≈500 m) has provided sediments to the Swiss Molasse Basin since at least 20 Ma. The southward migration of deformation in the Jura mountains suggests that the molasse basin started to uplift and exhume only after 5 Ma, as suggested also by previous authors. The data presented here show that the deformation of the whole region is occurring in an out-of-sequence trend, which is more likely associated with the reactivation of thrust faults beneath the foreland basin. This deformation trend suggests that tectonics is the most determinant factor controlling denudation and exhumation of the region, whereas the recently proposed “climate-induced exhumation” mechanism might play a secondary role.
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Trop, Jeffrey M., Jeffrey A. Benowitz, Donald Q. Koepp, David Sunderlin, Matthew E. Brueseke, Paul W. Layer, and Paul G. Fitzgerald. "Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault." Geosphere 16, no. 1 (November 21, 2019): 82–110. http://dx.doi.org/10.1130/ges02127.1.
Full textAbstract:
Abstract The Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone. These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska.
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Pisabarro, Alfonso, and Enrique Serrano Cañadas. "Chronology of geomorphological changes in a cantabrian mountain valley over the last 20,000 years." Cuaternario y Geomorfología 34, no. 3-4 (December 21, 2020): 61–78. http://dx.doi.org/10.17735/cyg.v34i3-4.86012.
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This is an in-depth study of a mixed deposit of terrace and alluvial fan in a valley of the Cantabrian Mountains that aims to characterize environmental conditions during the period following the Last Glacial Maximum (LGM) at the end of the Pleistocene and the entire Holocene, including human influence to the present day. In this perspective, the lithostratigraphy of different layers was described, the granulometric analysis performed in situ and in the laboratory, the organic bulk sediment dated by radiocarbon and weight, and other empirical studies, such as paleomagnetism were performed. The results reveal a temporal sequence of deposition from around 19.4 ky BP to the present showing different sedimentary environments. Paleoclimatical scientific literature in sorrounding areas complemented the interpretation of the results e.g. pleistocene glaciers, speleothems, palynology and geomorphology. We conclude a completely diferent evolution of studied section between Late-Pleistocene and Holocene. Bottom layers, composed of coarse boulders, are interpreted in the context of a second glacial push after the Local Last Glacial Maximum under conditions of torrentiality. In the upper layers, in the Holocene, there was an increase in sedimentation from slopes through alluvial and colluvial cones, and rivers lost their capacity to transport these sediments. Important environmental changes in the Middle Holocene, 5.5 ky BP, were detected with possible evidence of human action. A decrease from that moment in the deposited sediment caliber was verified.
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Boxberg, Florian, Sanja Asendorf, Alexander Bartholomä, Bernhard Schnetger, Willem P. de Lange, and Dierk Hebbeln. "Historical anthropogenic heavy metal input to the south-eastern North Sea." Geo-Marine Letters 40, no. 2 (September 9, 2019): 135–48. http://dx.doi.org/10.1007/s00367-019-00592-0.
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Abstract The Helgoland Mud Area (HMA) in the German Bight, covering an area of approximately 500 km2, is one of a few depocentres for finer sediments in the North Sea. Radiocarbon and 210Pb analyses revealed continuous sedimentation over the last several centuries. Zinc (Zn) and lead (Pb) contents in the sediments show a distinct increase towards the youngest most sediments with the thickness of the heavy metal enriched sediments ranging from 15 to 103 cm. Stratigraphic data indicate that the onset of heavy metal enrichment is diachronous progressing north-westward over the depocentre, paralleled by a decrease in the thickness of the enriched layer. Beginning already during medieval times, the enhanced input of Zn and Pb seemingly is related to silver and zinc mining in the Harz Mountains and the Erzgebirge, well-known mining areas since the Bronze Age. Both regions are directly connected to the HMA by the Elbe and Weser rivers. Zn and Pb enrichment began in the south-eastern HMA and progressed subsequently with an average of 10 m per year north-westward, most likely triggered by variations in river discharge and by the hydrodynamic setting. Quantitative assessments of the Zn and Pb content in the sediments suggest that since the onset of enhanced Zn and Pb deposition, the anthropic Zn and Pb input in the HMA amounts to ~ 12,000 t and ~ 4000 t, respectively.
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Strasser, Andre, and Elias Samankassou. "Carbonate Sedimentation Rates Today and in the Past: Holocene of Florida Bay, Bahamas, and Bermuda vs. Upper Jurassic and Lower Cretaceous of the Jura Mountains (Switzerland and France)." Geologia Croatica 56, no. 1 (2003): 1–18. http://dx.doi.org/10.4154/gc.2003.01.
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Lagoonal to intertidal sediments from the Holocene in Florida Bay,on the Bahamas, and in Bermuda are compared to similar facies in theKimmeridgian and Berriasian of the Swiss and French Jura Mountains.Dating by 14C permits the estimation of sediment accumulationrates in the Holocene. In the ancient outcrops, the timing is givenby cyclostratigraphic analysis. Elementary depositional sequencesformed in tune with the 20-ka precession cycle, although much ofthis time may have been spent in non-deposition and/or erosion. Afterdecompaction of the ancient sequences, their accumulation rates canbe evaluated. It is suggested that the studied Holocene sedimentsaccumulated over the past 6000 years with rates of 0.3 to 3 mm/a,whereas the Kimmeridgian and Berriasian facies show somewhatlower rates of 0.07 to 0.6 mm/a. This difference may be due to methodological errors, but also to variable carbonate production. In shallow carbonate systems, much of the sediment produced may be redistributed over the platform or exported. Furthermore, basin morphology and currents can strongly influence facies and thickness of the accumulated sediment. Finally, the accumulated sediment may suffer further erosion before it is preserved in the sedimentary record. Consequently, when estimating sedimentation rates in ancient sequences, it is important to do this with the highest time resolution possible, and only after having decompacted the sediment and evaluated the time lost in hiatuses or condensed intervals.
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Myrow, Paul M., Michael C. Pope, John W. Goodge, Woodward Fischer, and Alison R. Palmer. "Depositional history of pre-Devonian strata and timing of Ross orogenic tectonism in the central Transantarctic Mountains, Antarctica." GSA Bulletin 114, no. 9 (September 1, 2002): 1070–88. http://dx.doi.org/10.1130/0016-7606(2002)114<1070:dhopds>2.0.co;2.
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Abstract A combination of field mapping, detailed sedimentology, carbon isotope chemostratigraphy, and new paleontological finds provides a significantly improved understanding of the depositional and tectonic history of uppermost Neoproterozoic and lower Paleozoic strata of the central Trans ant arc tic Mountains. On the basis of these data, we suggest revision of the existing stratigraphy, including introduction of new formations, as follows. The oldest rocks appear to record late Neoproterozoic deposition across a narrow marine margin underlain by Precambrian basement. Siliciclastic deposits of the Neoproterozoic Beardmore Group—here restricted to the Cobham Formation and those rocks of the Goldie Formation that contain no detrital components younger than ca. 600 Ma—occupied an inboard zone to the west. They consist of shallow-marine deposits of an uncertain tectonic setting, although it was likely a rift to passive margin. Most rocks previously mapped as Goldie Formation are in fact Cambrian in age or younger, and we reassign them to the Starshot Formation of the Byrd Group; this change reduces the exposed area of the Goldie Formation to a small fraction of its previous extent. The basal unit of the Byrd Group—the predominantly carbonate ramp deposits of the Shackleton Limestone—rest with presumed unconformity on the restricted Goldie Formation. Paleontological data and carbon isotope stratigraphy indicate that the Lower Cambrian Shackleton Limestone ranges from lower Atdabanian through upper Botomian. This study presents the first description of a depositional contact between the Shackleton Limestone and overlying clastic units of the upper Byrd Group. This carbonate-to-clastic transition is of critical importance because it records a profound shift in the tectonic and depositional history of the region, namely from relatively passive sedimentation to active uplift and erosion associated with the Ross orogeny. The uppermost Shackleton Limestone is capped by a set of archaeocyathan bioherms with up to 40 m of relief above the seafloor. A widespread phosphatic crust on the bio herms records the onset of orogenesis and drowning of the carbonate ramp. A newly defined transitional unit, the Holyoake Formation, rests above this surface. It consists of black shale followed by mixed nodular carbonate and shale that fill in between, and just barely above, the tallest of the bioherms. This formation grades upward into trilobite- and hyolithid-bearing calcareous siltstone of the Starshot Formation and alluvial-fan deposits of the Douglas Conglomerate. Trilobite fauna from the lowermost siltstone deposits of the Starshot Formation date the onset of this transition as being late Botomian. The abrupt transition from the Shackleton Limestone to a large-scale, upward-coarsening siliciclastic succession records deepening of the outer platform and then deposition of an eastward-prograding molassic wedge. The various formations of the upper Byrd Group show general stratigraphic and age equivalence, such that coarse-grained alluvial-fan deposits of the Douglas Conglomerate are proximal equivalents of the marginal-marine to shelf deposits of the Starshot Formation. Paleocurrents and facies distributions from these units indicate consistent west (or southwest) to east (or northeast) transport of sediment. Although the exact structural geometry is unknown, development of imbricate thrust sheets in the west likely caused depression of the inner margin and rapid drowning of the Shackleton Formation carbonate ramp. This tectonic activity also caused uplift of the inboard units and their underlying basement, unroofing, and widespread deposition of a thick, coarse clastic wedge. Continued deformation in the Early Ordovician (younger than 480 Ma) in turn affected these synorogenic deposits, causing folding and thrust repetition of all pre- Devonian units.
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Harris, Brette S., Maya T. LaGrange, Sara K. Biddle, Tiffany L. Playter, Kathryn M. Fiess, and Murray K. Gingras. "Chemostratigraphy as a tool for sequence stratigraphy in the Devonian Hare Indian Formation in the Mackenzie Mountains and Central Mackenzie Valley, Northwest Territories, Canada." Canadian Journal of Earth Sciences 59, no. 1 (January 2022): 29–45. http://dx.doi.org/10.1139/cjes-2020-0198.
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The Hare Indian Formation (HIF) is a late Eifelian to Givetian organic-rich mudstone constituting the lower portion of the Horn River Group (HRG), which has been minimally scrutinized in the literature. This paper proposes depositional environments and a sequence stratigraphic framework for the HIF. Using composition data collected via energy-dispersive X-ray fluorescence, geochemical proxies inform detrital input, silica source, and paleoredox conditions. Cross-plots and chemostratigraphic profiles of detritally sourced Al, Ti, and K and redox-sensitive Mo and V inform depositional and stratigraphic constraints. Silica proportions vary, indicating that sediment was derived from detrital and biogenic sources. Al, Ti, and K distributions increase upwards, showing increased continentally sourced minerals. Redox-sensitive metals are highest in the Bluefish Member (BM), suggesting intermittent euxinia. Based on the presence of continental and pelagic sediments, the sedimentary environment is interpreted as proximal- to mid-shelf. These proxies guide systems tract interpretations. Si and redox-sensitive metal concentrations peak higher in the BM, accompanied by lowered concentrations of Al, Ti, and K, suggesting a maximum flooding surface. At the top of the Prohibition and Bell Creek members, redox-sensitive enrichments are lower with higher concentrations of Al, Ti, and K, suggesting a maximum regressive surface. Transgression occurred during the initial deposition of the BM, followed by regression for the remainder of the HIF. The sedimentology of the HIF can be difficult to decipher; the use of chemostratigraphy supports its geological history (including sedimentation trends and a local record of relative sea level) using methods that may be applied to other fine-grained successions.
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Etemad-Saeed, Najmeh, Mahdi Najafi, and Negar Nasirizadeh. "Oligocene–late Miocene basin evolution in the Yengejeh syncline in the Central Iranian Basin in response to the Arabia–Eurasia orogeny." Journal of Sedimentary Research 92, no. 9 (September 22, 2022): 836–57. http://dx.doi.org/10.2110/jsr.2021.140.
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Abstract The Central Iranian Basin has developed during a multi-episodic collision between the Arabian and Eurasian continents since the late Eocene–early Oligocene, following the subduction of the Neo-Tethys Ocean. Herein, we present detailed sedimentological and provenance data of the Oligocene–upper Miocene synorogenic strata, including the unconformity-bounded Lower Red, Qom, and Upper Red formations, in the Yengejeh syncline in the NW termination of Central Iran, to analyze stratigraphy, depositional environments, and provenance. Our results indicate that the sedimentary system has evolved in five stages coeval with regional deformational and volcanic events: a) deposition of the Lower Red Formation in an alluvial fan containing the first appearance of Sanandaj–Sirjan metamorphic clasts sourced from the proximal southwestern Takab Complex, exhumed by the onset of Arabian–Eurasian soft collision in late Eocene–early Oligocene; b) Burdigalian transgression of the Qom Sea and shallow-water carbonate sedimentation influenced by continuous pyroclastic inputs and lava flows from an active volcanic center; c) deposition of the M1 unit of the Upper Red Formation in a continental sabkha in arid climate conditions during Burdigalian–Langhian and the first appearance of internal clasts derived from the folded Qom Formation layers due to the Arabian–Eurasian hard collision; d) fluvial deposition of the M2 unit during the Langhian–Tortonian with sediments derived from the Qom Formation and Takab Complex; and e) deposition of the uppermost siliciclastics of the M2 unit at the edge of an alluvial fan during the late Miocene, after a period of pyroclastic fallout in the Tortonian. In general, the source-to-sink relationship is controlled by the development of tectono-topographic relief in the crystalline core of the Zagros Mountains that configured the source areas in the Sanandaj–Sirjan metamorphic belt supplying the NW termination of Central Iran through a well-developed drainage system towards the Caspian Sea. Coeval with the deformational events, magmatic phases supplied a large volume of volcaniclastic inputs both before the Neo-Tethys slab break-off and after the hard continental collision. The depositional environments and provenance of the studied sedimentary record provide an analog for the development of synorogenic hinterland basins worldwide along with the well-known Altiplano Basin of the Andes and Hoh Xil Basin of Tibet.
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BRADSHAW, JOHN D., ALAN P. M. VAUGHAN, IAN L. MILLAR, MICHAEL J. FLOWERDEW, RUDOLPH A. J. TROUW, C. MARK FANNING, and MARTIN J. WHITEHOUSE. "Permo-Carboniferous conglomerates in the Trinity Peninsula Group at View Point, Antarctic Peninsula: sedimentology, geochronology and isotope evidence for provenance and tectonic setting in Gondwana." Geological Magazine 149, no. 4 (October 24, 2011): 626–44. http://dx.doi.org/10.1017/s001675681100080x.
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AbstractField observations from the Trinity Peninsula Group at View Point on the Antarctic Peninsula indicate that thick, southward-younging and overturned clastic sedimentary rocks, comprising unusually coarse conglomeratic lenses within a succession of fine-grained sandstone–mudstone couplets, are the deposits of debris and turbidity flows on or at the foot of a submarine slope. Three detrital zircons from the sandstone–mudstone couplets date deposition at 302 ± 3 Ma, at or shortly after the Carboniferous–Permian boundary. Conglomerates predominantly consist of quartzite and granite and contain boulders exceeding 500 mm in diameter. Zircons from granitoid clasts and a silicic volcanic clast yield U–Pb ages of 466 ± 3 Ma, 373 ± 5 Ma and 487 ± 4 Ma, respectively and have corresponding average εHft values between +0.3 and +7.6. A quartzite clast, conglomerate matrix and sandstone interbedded with the conglomerate units have broadly similar detrital zircon age distributions and Hf isotope compositions. The clast and detrital zircon ages match well with sources within Patagonia; however, the age of one granite clast and the εHf characteristics of some detrital zircons point to a lesser South Africa or Ellsworth Mountain-like contribution, and the quartzite and granite-dominated composition of the conglomerates is similar to upper Palaeozoic diamictites in the Ellsworth Mountains. Unlike detrital zircons, large conglomerate clasts limit possible transport distance, and suggest sedimentation took place on or near the edge of continental crust. Comparison with other upper Palaeozoic to Mesozoic sediments in the Antarctic Peninsula and Patagonia, including detrital zircon composition and the style of deformation, suggests deposition of the Trinity Peninsula Group in an upper plate basin on an active margin, rather than a subduction-related accretionary setting, with slow extension and rifting punctuated by short periods of compression.
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Brandano, Marco, Irene Cornacchia, and Rita Catanzariti. "Fault-Block Platform Evolution between Late Cretaceous and Early Miocene along the Margin of the Latium-Abruzzi Carbonate Platform (Southern Prenestini Mountains, Central Apennines, Italy)." Geosciences 12, no. 9 (September 19, 2022): 348. http://dx.doi.org/10.3390/geosciences12090348.
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Since the origin of the carbonate platform concept, the reconstruction of the geometry and the evolution of the margin has been an intriguing topic. The Latium-Abruzzi platform is one of the largest shallow water domains of the Central Apennines, however, the reconstruction of the geometry and evolution of its margin has been classically problematic because the latter has been erased by the out-of-sequence Olevano-Antrodoco thrust system. The investigated area is placed in the Prenestini Mountains, the southernmost portion of the Sabina Domain, where a Cretaceous to Neogene carbonate succession, ascribed the Latium-Abruzzi platform margin, crops out. Stratigraphic and facies analyses showed a Late Cretaceous extensional stage that produced two main fault-block platforms, respectively, South Eastern Prenestini and South Western Prenestini platforms, developed westward of the large Latium-Abruzzi Platform domain. In these platforms, during the Paleocene–Eocene interval, pelagite deposition coincides with the main relative sea-level rise. Instead, during the following falling stage, the seafloor, consisting of the Cretaceous carbonate, was in the wave abrasion zone and the pelagic carbonate mud was swept away or trapped in local depressions or fractures (neptunian dykes), whereas the coarse sediment produced by the erosion of indented and fractured substrate formed polygenic conglomerate accumulation on the Cretaceuos carbonate platform substrate. Successively, an isolated homoclinal ramp, the Guadagnolo Fm, Aquitanian to Serravallian in age, developed on the drowned fault-block platforms, suggesting that during Neogene the articulation of the substrate of the two fault-block platforms had to be limited to host the bioclastic sedimentation of the Guadagnolo Fm and to allow the development of a carbonate ramp depositional profile.
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Gestain, Vincent, Thierry Nalpas, Delphine Rouby, and Laurie Barrier. "Role of synkinematic ductile levels on the evolution of compressive zones – analogue modelling." Bulletin de la Société Géologique de France 175, no. 4 (July 1, 2004): 351–59. http://dx.doi.org/10.2113/175.4.351.
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Abstract In foldbelt faults, layers with ductile behaviour can form levels of décollement [Byerlee, 1978]. When these levels are prekinematic, they play a significant role in the genesis, evolution and final geometry of the foldbelt faults, as, for example in the Appalachian Mountains [Davis and Engelder, 1985], the Jura [Sommaruga, 1999], or the Pyrenees [Vergés et al., 1992]. Previous studies based on analogue modelling have shown how a prekinematic décollement level can influence the geometry of foldbelt faults and structures [Ballard, 1989; Colletta et al., 1991; Letouzey et al., 1995; Merle et Abidi, 1995]. However, no study has yet described the influence of synkinematic sedimentation of incompetent levels on the genesis and evolution of compressive structures. The laboratory experiments presented here are designed to explore some of the mechanisms of formation of synsedimentary thrust faults, in relation with the occurrence of a décollement layer during syntectonic sedimentation. Analogue modelling – Experimental procedure The models presented here were designed to simulate geological situations comparable to those observed on the border of an overthrust belt. The modelling techniques are similar to those usually applied in experiments on brittle-ductile systems at the Laboratory of Experimental Tectonics of the Geosciences department (Rennes University), and have been fully described in previous studies [e.g. Faugère and Brun, 1984; Vendeville et al., 1987; Davy and Cobbold, 1991]. The prekinematic and synkinematic brittle levels are represented by sand, while the prekinematic and synkinematic ductile levels are represented by silicone. The experimental apparatus is composed of a fixed and rigid basal plate over which a thin mobile plate is pushed at a constant rate. During shortening (of 5 cm), brittle sedimentation is simulated by sprinkling fresh sand onto the model, and ductile sedimentation is simulated by the deposition of a thin silicone plate onto the model. Photographs of the model surface are taken at regular time intervals to study the development of the structures. The internal structure is recorded from serial cross-sections cut after the experiments. The parameters tested are the sedimentation rate [see also Tondji Biyo, 1995; Nalpas et al., 1999; Barrier et al., 2002], and the presence and location of a synkinematic décollement layer. The sedimentation is homogeneously distributed on both sides of the relief developed above the thrust front, with a variable ratio R between the rate of sedimentation (vsed) and the rate of uplift (vup), with R taking the values (1) R = vsed/vup = 1/2, (2) R = 1 and (3) R = 2 [Barrier et al., 2002]. The décollement level is deposited at the beginning of sedimentation, either over the whole model or in front of the thrust throughout sedimentation. Results In all models, the progressive shortening is accommodated by two conjugate reverse faults. The major fault is antithetic to the displacement of the mobile wall. The synthetic fault is transitory [Ballard, 1989; Tondji Biyo, 1995]. In experiments without ductile sedimentation, the main thrust zone shows an increasing dip with each depositional increment [Barrier et al., 2002]. When the ductile level is deposited, (1) the dip of the main thrust decreases as it reaches the silicone, (2) a wedge of sand then penetrates the silicone forming a detachment, and (3) this wedge is abandoned and the main thrust fault cuts through the wedge, allowing the fault to propagate upward. At low sedimentation rate, the final geometry shows a major reverse fault made up of a ramp in the prekinematic sand and a flat in the synkinematic silicone. At high sedimentation rate, the major reverse fault is made up of a ramp in the prekinematic sand and a flat in the synkinematic silicone forming a distinctive wedge of sand and a prolongation of the ramp rear the sand wedge. The presence of a synkinematic ductile level in the model at the beginning of shortening favours decoupling between the prekinematic and the synkinematic sand: the faults in the prekinematic sand are not directly connected to the faults in the synkinematic sand. In addition, the deformation of the sand is different according to whether it is underneath or above the synkinematic ductile level. The prekinematic or synkinematic sand under the synkinematic ductile level is undeformed, whereas the synkinematic sand overlying the synkinematic ductile level is folded. Discussion In the presence of a ductile level, the reverse fault forms a flat in the silicone. The silicone leads to different behaviours of the fault and the synkinematic sand. This raises the question of how to identify synkinematic deposits in compressive basins. In most cases, only the geometry of the strata is used: if progressive unconformity is observed, the strata are synkinematic (growth strata), if not, the strata are deposited before or after the deformation. However, the evolution of growth-strata geometry is also related to the rheology of the rocks. Since geometrical criteria are insufficient, it is also necessary to take account of facies variations. Conclusions The presence of a synkinematic ductile level results in the development of a low angle thrust. The presence of synkinematic ductile levels facilitates deformation and the development of progressive unconformity in growth strata. Synkinematic sediments with brittle behaviour, deposited in front of a thrust fault, cannot develop a progressive unconformity. The absence of a progressive unconformity does not necessarily rule out a formation being synkinematic.
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Van Staal, Cees R., Alexandre Zagorevski, Vicki J. McNicoll, and Neil Rogers. "Time-Transgressive Salinic and Acadian Orogenesis, Magmatism and Old Red Sandstone Sedimentation in Newfoundland." Geoscience Canada 41, no. 2 (May 7, 2014): 138. http://dx.doi.org/10.12789/geocanj.2014.41.031.
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We propose an intimate relationship between Silurian terrestrial red bed sedimentation (Old Red Sandstone), slab breakoff-related magmatism and deformation in the Newfoundland Appalachians. Red bed sedimentation started during the Early Silurian, and records the progressive rise of the Salinic mountains in the tectonic hinterland of the orogen. The red beds were mainly deposited in molasse-style foreland basins in front of an east-propagating terminal Salinic deformation front. New U–Pb zircon dating of volcanic rocks interlayered with the Silurian red beds in key structural locations yielded ages ranging between 425 and 418 Ma, which, combined with the existing geochronological database, suggests that the sedimentary rocks are progressively younger from west to east and overstep the accreted Gondwana-derived terranes. We propose that deposition of the red beds is a good proxy for the time of cratonization of the accreted terranes. Eastward migration of the Salinic deformation front was accompanied by eastward-widening of a slab-breakoff-related asthenospheric window. The latter is interpreted to have formed due to a combination of progressive steepening of the down-going plate following entrance of the leading edge of the Gander margin and its eduction. Gander margin eduction (reversed subduction) is proposed to have been instigated by the trench migration of the Acadian coastal arc built upon the trailing edge of the Gander margin, which developed contemporaneously with the Salinic collision. The resultant thinning of the lithosphere beneath the Salinic orogen, built upon the leading edge of the Gander margin immediately prior to the onset of the Early Devonian Acadian orogeny, set the stage for generation of the widespread bloom of Acadian magmatism.SOMMAIRENous proposons qu’il y a eu une relation intime entre la sédimentation des couches rouges continentales au Silurien (vieux-grès-rouges), un magmatisme lié à une rupture de segments de croûte, et la déformation appalachienne à Terre-Neuve. La sédimentation des couches rouges qui a débuté au début du Silurien témoigne du soulèvement progressif des monts saliniques de l’arrière-pays tectonique de l’orogène. Les couches rouges se sont déposées sous forme de molasses dans des bassins d’avant-pays, à l’avant du front de déformation salinique terminale qui se déployait vers l’est. De nouvelles datations U-Pb sur zircon de roches volcaniques interstratifiées avec des couches rouges siluriennes en des lieux structurels stratégiques montrent des âges qui varient entre 425 Ma et 418 Ma, ce qui, combiné aux bases de données géochronologiques existantes permet de penser que les roches sédimentaires sont progressivement plus jeunes d’ouest en est, et qu’elles surplombent les terranes accrétés du Gondwana. Nous suggérons que les couches rouges sont de bons indicateurs temporels de la cratonisation des terranes accrétés. La migration vers l’est du front de la déformation salinique a été accompagnée par un élargissement vers l’est d’une fenêtre asthénosphérique liée à une rupture de la croûte. Cette dernière aurait été provoquée par la combinaison de l’enfoncement progressif de la plaque qui a suivi l’entrée du bord d’attaque de la marge de Gander, et son éduction. Nous proposons que l’éduction (l’inverse de la subduction) de la marge de Gander a été provoquée par la migration de la fosse tectonique côtière acadienne, induite par la migration du bord d’attaque de la marge de Gander, contemporaine de la collision salinique. L’amincissement de la lithosphère sous l’orogène salinique qui en a résulté, et qui s’est déployé au bord d’attaque de la marge de Gander juste avant l’enclenchement de l’orogénie acadienne au début du Dévonien, a préparé le terrain du déploiement à grande échelle du magmatisme acadien.
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Hughes, G. Wyn, David J. Grainger, Abdul-Jaleel Abu-Bshait, and M. Jarad Abdul-Rahman. "Lithostratigraphy and Depositional History of Part of the Midyan Region, Northwestern Saudi Arabia." GeoArabia 4, no. 4 (October 1, 1999): 503–42. http://dx.doi.org/10.2113/geoarabia0404503.
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ABSTRACT The Midyan region provides a unique opportunity in which to examine exposures of the Upper Cretaceous and Neogene sedimentary succession. Recent investigations have yielded new interpretations of its depositional environments, stratigraphic relationships, and structure. In this paper, all the lithostratigraphic units of the Midyan succession are considered to be informal in advance of an on-going process of formalization. The region is bounded to the north and northeast by mountains of Proterozoic rocks and to the west and south by the Gulf of Aqaba and the Red Sea, respectively. The Wadi Ifal plain occupies most of the eastern half of the region, beneath which is a thick sedimentary succession within the Ifal basin. The oldest sedimentary rocks are the fluviatile Upper Cretaceous Adaffa formation and marine siliciclastics and carbonates of the lower Miocene Tayran group, unconformable on the Proterozoic basement. The Tayran group is unconformably overlain by the deep-marine lower Miocene Burqan formation that, in turn, is overlain by marine mudstones, carbonates, and evaporites of the middle Miocene Maqna group. The poorly exposed middle Miocene Mansiyah and middle to upper Miocene Ghawwas formations consist of marine evaporites and shallow to marginal marine sediments, respectively. The youngest rocks are alluvial sands and gravels of the Pliocene Lisan formation. A complex structural history is due to Red Sea Oligocene-Miocene extension tectonics, and Pliocene-Recent anti-clockwise rotation of the Arabian Plate relative to Africa on the Dead Sea Transform Fault. The Upper Cretaceous succession is a probable pre-rift unit. The Oligocene?-Miocene syn-rift 1 phase of continental extension caused slow subsidence (Tayran group). Syn-rift 2 was an early Miocene phase of rapid subsidence (Burqan formation) whereas syn-rift 3 (early to middle Miocene) was another phase of slow deposition (Maqna group). The middle to late Miocene syn-rift 4 phase coincided with the deposition of the Mansiyah and Ghawwas formations. The Lower Pliocene to Recent succession is related to the drift (post-rift) phase during which about 45 kilometers of sinistral movement occurred on the Dead Sea Fault. The structural control on sedimentation is evident: the Ifal basin was formed by east-west lithospheric extension; pull-apart basins occur along major left-lateral faults on the eastern coast of the Gulf of Aqaba; and basin-bounding faults controlled deposition of the Burqan, Ghawwas, and Lisan formations. Pliocene to Recent earth movements may be responsible for activating salt diapirism in the Ifal basin. Extensive Quaternary faulting and regional uplift caused the uplift of coral reefs to at least 6 to 8 meters above sea level.
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McNeil, D. H., J. Dixon, Z. Xiu, and S. P. Fowler. "Lithostratigraphic revision and biostratigraphy of Upper Hauterivian–Barremian strata from the Kugmallit Trough, Mackenzie Delta, Northwest Territories." Bulletin of Canadian Petroleum Geology 68, no. 4 (December 1, 2020): 141–57. http://dx.doi.org/10.35767/gscpgbull.68.4.141.
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Abstract The Kipnik Formation, named herein, is defined from the Late Hauterivian to Barremian Kugmallit Trough in the Mackenzie Delta, Arctic Canada. The trough was formed by extensional tectonics associated with the opening of the Canada Basin and was infilled by kilometre-thick accumulations of clastic sediments. Samples from the Kugmallit Trough are known only from two exploration wells – Shell Kipnik O-20 and Gulf Mobil Ogruknang M-31. Examination of palynomorphs, foraminifera, and ostracods from cuttings of these wells, integrated with regional subsurface and outcrop correlations, indicated that the existing subsurface stratigraphic interpretations [Upper Jurassic to Barremian] of the Kugmallit Trough were in need of revision. The revised Upper Hauterivian–Barremian succession thus consists of the Siku, Kipnik (new), and Mount Goodenough formations. The Siku and Kipnik formations are known only from the subsurface, but the Mt. Goodenough Formation is widespread and was deposited over a regional unconformity. The Siku to Kipnik deposition is a large-scale transgressive-regressive succession that represents deposition during a period of initial subsidence (transgression) followed by uplift and erosion (regression). The shale dominant Siku Formation contains a distinctive unnamed foraminiferal assemblage that consists of agglutinated species typical of offshore or deeper water. Ostracods of the Siku Formation are contained in the informal Galliaecytheridea postsinuata zone, which is confined to the Siku Formation. Ostracods of the G. postsinuata zone suggest shelf environments. The Kipnik Formation is sand-dominant with thin beds of shale, siltstone and coal. Agglutinated foraminifera occur sparsely because of coarse, rapid sedimentation. Inner shelf environments are suggested by the foraminifera. The lower half of the Mount Goodenough Formation is shale-dominant and the upper half consists of intercalated shale and sandstone. Foraminifera and ostracods occur abundantly in the Mt. Goodenough subsurface and outcrops of the Richardson Mountains. The foraminiferal Convallina mcneili Zone of Barremian age occurs in the Mt. -Goodenough Formation and its composition of agglutinated and calcareous benthic foraminifera suggests outer shelf or deeper environments. Ostracods of the Mt. Goodenough Formation in subsurface and outcrop are assigned to the informal Clithrocytheridea spp. zone. Ostracods suggest an outer shelf or deeper-water environment. Palynomorphs indicate that the Siku Formation is Late Hauterivian, the Kipnik Formation is probably latest Hauterivian to Early Barremian, and the Mount Goodenough Formation is Barremian.
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Pazdur, Anna, Tomasz Goslar, Mirosława Pawlyta, Helena Hercman, and Michał Gradziński. "Variations of Isotopic Composition of Carbon in the Karst Environment from Southern Poland, Present and Past." Radiocarbon 41, no. 1 (1999): 81–97. http://dx.doi.org/10.1017/s0033822200019354.
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We describe a comprehensive study of carbon isotopes in several karst springs and their environs in a contemporary karst environment in the region of the Cracow-Wieluñ Upland and Western Tatra Mountains, Southern Poland. We collected samples of water, plants and carbonate deposited on aquatic plants, and obtained 13C values and 14C concentrations. We also investigated a group of the youngest calcium carbonates from caves where deposition is still being observed or ceased no more than a few hundred years ago. The determination of a 14C dilution factor (q) in these carbonates allows us to determine the “true” radiocarbon ages of old speleothems from caves in the area under investigation and enables the use of old speleothems as suitable material for extending the 14C calibration time scale, the “Absolute” age having been determined by U/Th or amino acid racemization (AAR) dating methods. Measurements of δ13C and 14C concentrations were made on dissolved inorganic carbon (DIC) extracted from water samples. Calculated values of q range from 0.55 to 0.68 and δ13C values range from −10% to −13% versus VPDB with mean values equal to 0.65 and −12%, respectively. Results indicate that the dissolution process of limestone bedrock is a closed system with the dominating contributor being biogenic carbon dioxide.Isotopic composition of carbon in contemporary plants collected at the karstic springs at 3 localities is highly diverse, with different species distinctly varying in both q and δ13C values. Extremely light values of 13C (under −40%), observed in Algae and Hyloconium splendens, are correlated with 14C concentrations that are much lower than 100 pMC. Small systematic changes of isotopic composition were found in plants of the same species collected along streams at various distances from the spring. The youngest calcium carbonates from different caves show a relatively high scatter of both δ13C values and 14C concentration. The lower reservoir effect for 14C is observed in samples with higher value of δ13C, indicating equilibrium conditions in the sedimentation of carbonate. Pazdur et al. (1995b) presented 14C dating results and paleoclimatic interpretation of 170 14C analyses of 89 speleothems from 41 caves obtained through 1994. Investigations continued until early 1997, during which time a speleothem, JWi2, was dated by 14C, U/Th and AAR dating methods, and its stable isotope composition (δ13C and δ18O) analyzed in detail (reported here). Carbon isotope analyses indicate very large differences among results obtained by U/Th, AAR, and 14C dating methods.
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Zhou, Zaizheng, Junling Pei, Jianfeng Li, Yuhang Cai, and Lifu Hou. "High-resolution magnetostratigraphic records of the pliocene sedimentary successions in Yengisar section, NW China, and its tectonic implications." Frontiers in Earth Science 10 (August 15, 2022). http://dx.doi.org/10.3389/feart.2022.967346.
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The Neogene strata upward-coarsening sandstone and conglomerate sequences at the periphery of the Northeastern Pamir record the intense uplift of the paleosurface of the building mountains. To further improve our knowledge of source-sink processes, a detailed magnetostratigraphic investigation was carried out along the Yengisar section, which is located at the southwestern margin of the Tarim Basin. The new high-resolution magnetostratigraphic data revealed that the Artux Formation was deposited from 4.9 Ma to 1.9 Ma with three sedimentation rates changes. The variations in sedimentation rate may be due to the pulsating exhumation of the Western Kunlun Mountain, caused by the northward motion of the Pamir salient. By integrating the evidences from the seismic reflection profile and other magnetostratigraphic investigations in this region, the basal age of the Xiyu Formation and the early stages of growth strata deposition were estimated at ∼1.9 and 1.45 Ma, respectively. Based on the data, we propose that the progradation of the Xiyu Formation and the migration of the deformation front are the two independent responses of the sink region to the uplift events of the source region.
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Szarłowicz, Katarzyna, Marcin Stobiński, Filip Jedrzejek, and Barbara Kubica. "Sedimentary conditions based on the vertical distribution of radionuclides in small dystrophic lakes: a case study of Toporowe Stawy Lakes (Tatra Mountains, Poland)." Environmental Science and Pollution Research, July 19, 2022. http://dx.doi.org/10.1007/s11356-022-21922-3.
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AbstractThe aim of this work was to prove the use of radionuclides deposited in sediment core taken from an overgrowing dystrophic lakes surrounded by marsh-peat vegetation to estimate sedimentary conditions. Sediment core samples were taken from the Toporowe Stawy Lakes (Niżni (TSN) and Wyżni (TSW); Tatra Mountains). The sampling was done using a Limnos corer. After the physical sample preparations, gamma measurements were performed. Radiochemical analysis was applied with the aim of determining 210Pb radioactivity by means of 210Po. The mean values for TSN lake are as follows: 137Cs ~ 123 Bq∙kg−1, 40 K ~ 389 Bq∙kg−1, 228Th ~ 55 Bq∙kg−1, 226Ra ~ 86 Bq∙kg−1, 241Am ~ 5 Bq∙kg−1, and 210Pbuns ~ 180 Bq∙kg−1. For TSW lake, the radioactivity levels of 226Ra and 241Am are comparable to the TSN. The mean values of 137Cs, 40 K, and 228Th are almost twice as high as in TSN. The level of 210Pb in uppermost layer of TSN is higher than in TSW. Sediments were dated by use of 210Pb method, and the rate of sedimentation of each layer was also estimated. Basic chemometric tools were used to confirm the way of deposition of radionuclide, find the correlations between variables, and compare analyzed lakes. It was concluded that the presented type of lakes are a valuable source of information and the vertical distribution of radionuclide can be used to interpret the source of material supply and factors that influence the sedimentation process in recent 150–200 years.
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Cerri, Rodrigo I., Lucas V. Warren, Filipe G. Varejão, Alex J. Choupina A. Silva, Cristiano Lana, and Mario L. Assine. "So close and yet so far: U–Pb geochronological constraints of the Jaibaras Rift Basin and the intracratonic Parnaíba Basin in SW Gondwana." Geological Magazine, April 6, 2021, 1–21. http://dx.doi.org/10.1017/s0016756821000236.
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Abstract Several sag-type basins apparently developed from rift systems, but there is no consensus about how and if these grabens influenced the sedimentation of the post-rift thermal subsidence phase. The Ediacaran Jaibaras Rift Basin is one of the best-exposed sedimentary records among the NE Brazil late Precambrian – early Cambrian rift system, cropping out at the eastern margin of the intracratonic Parnaíba Basin and extending below it towards the west. Here we present detrital zircon U–Pb ages of rocks from the Jaibaras (Aprazível Formation) and Parnaíba (Ipu Formation) basins, in order to understand the provenance patterns, maximum depositional ages (MDA) and age relationship between these units. The MDA for the Aprazível Formation (c. 499 ± 5 Ma) indicates a Cambrian age for the upper part of the Jaibaras Basin. The bulk U–Pb data indicate that the Ipu Formation started to deposit during late Cambrian and/or Early Ordovician time, despite its MDA (c. 528 ± 11 Ma) being older than that of the Aprazível Formation. Detrital zircon provenance suggests that the primary source areas for the early deposits of the Parnaíba Basin were mountains related to the Brasiliano Orogeny to the south and SE (e.g. Rio Preto and Riacho do Pontal metamorphic belts). Finally, our data emphasize the key change in source areas from the rift to the initial deposition of the intracratonic phase, indicating major depositional style changes between both basins after the Gondwana assembly.
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Faisal, B. M. Refat, and Yuichi S. Hayakawa. "Geomorphological processes and their connectivity in hillslope, fluvial, and coastal areas in Bangladesh: A review." Progress in Earth and Planetary Science 9, no. 1 (July 25, 2022). http://dx.doi.org/10.1186/s40645-022-00500-8.
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Abstract Geomorphological knowledge is critical in understanding watershed scale surface processes, including steep mountainous areas and flat lowlands, particularly if the mid- and downstream areas are densely populated and hazard assessments are highly required. However, our knowledge about such surface processes has relatively been limited in some areas in South Asia due likely to the lack of comprehensive studies of geomorphology and related fields. This article undertakes an overview of the geomorphological processes of the disaster-prone deltaic landscape of the Ganges–Brahmaputra–Meghna (GBM), particularly focusing on fluvial processes. The area locates in the downstream of the watershed system including Himalayan Mountains and highly connected with the upper basin morphodynamics, hydrology, and sediment flux. The previous studies are summarized at different geomorphic settings concerning hillslopes, fluvial plains, and coastal areas to provide clarity about the geomorphic processes linking erosion-prone upstream source areas to deposition-dominated downstream areas. The review found that most of the geomorphic researches in Bangladesh are exploring landslide inventory and susceptibility mapping in hilly areas; river channel or riverbank shifting, riverbank erosion and accretion in fluvial environments; watershed morphometric analysis and geomorphic unit identification in plain land; and coastline shifting or coastal erosion and accretion in coastal environments at a small scale. Then, we discuss the fluvial dynamics and sediment transport of the GBM river system to address the knowledge gap in the context of deltaic plain land in Bangladesh, where upstream fluvial sedimentation processes impact the geomorphic connectivity from Himalayan to the Bay of Bengal. Although some studies on the fluvial dynamics and sediment dispersal in the upstream GBM river basin are present, the fluvial processes in the downstream domain of Bangladesh are not fully understood with a limited number of research with field-based approaches. Some future perspectives of geomorphic research in Bangladesh are then mentioned to understand better the complex geomorphological settings in the entire GBM watershed and to strengthen the existing research capacity. This review will also develop a holistic understanding of fluvial geomorphic processes of the GBM River to the policymakers and may be helpful to improve the transboundary river basin management policies or strategies.
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De Wit, Maarten J., Bastien Linol, and Vhuhwavhohau Nengovhela. "Proterozoic–Paleozoic Sedimentary Rocks and Mesozoic–Cenozoic Landscapes of the Cape Mountains Across the Kango Complex Reveal ‘More Gaps Than Record’ from Rodinia and Gondwana to Africa." Geoscience Canada, July 10, 2020, 7–58. http://dx.doi.org/10.12789/geocanj.2020.47.157.
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The Kango (Cango) region flanks the northern margins of the Klein Karoo and the Cape Mountains across the Western Cape Province of South Africa. It preserves a condensed Proterozoic–Paleozoic stratigraphy exposed via a Mesozoic–Cenozoic morphology with a present Alpine-like topography. Its rocks and landscapes have been repeatedly mapped and documented for the past 150 years. Over the last 25 years, we remapped and dated a central-eastern section of this region. The subvertically bedded and cleaved rocks reveal an 8–10 km thick stratigraphy covering more than 700 million years between ca. 1200 and 500 Ma with several unconformities and disconformities. At ca. 252 Ma, during the Cape orogeny, this Kango Complex was deformed along thrusts and sub-isoclinal folds producing steeply dipping phyllites and slates. It was uplifted by 3–5 km during the Kalahari epeirogeny between 140 and 60 Ma while eroding at ca. 100–200 m/m.y. (120–80 Ma). During the Cenozoic, the rate of uplift decreased by an order of magnitude and today is ca. 0.4–0.7 m/m.y. across steep slopes and canyons in contrast to the Himalayas where erosion rates are about hundred times faster. A recent publication about this central-eastern section of the Kango region disputes the existence of regional isoclinal folds and suggests that deposition of the oldest sedimentary successions, including carbonate rocks of the Cango Caves (limestone-marble with enigmatic microfossils) was simple, continuous and restricted to between ca. 700 and 500 Ma, decreasing earlier estimates of the stratigraphic age range by 60–80%. Similarly, recent interpretations of the complex landscapes link the northern contact between the Kango and Table Mountain rock sequences to Quaternary faults. We present a new geological database, mapped between 1:500 and 1:10,000 scales, and twelve stratigraphic sections with younging directions linked to structural and isotopic data that support repetitions along regional isoclinal folds and thrust zones of the Kango sequences during the Permo–Triassic Cape orogeny, and geomorphic data that link the origin of its landscapes to weathering and erosion during the Cretaceous–Cenozoic Kalahari epeirogeny. During its evolution, the Kango Basin directly flanked both Grenvillian and Pan-African Mountain systems. But, at an average sedimentation rate of ca. 1 mm/70 years (0.014 mm/year) and with present low erosion rates (0.005 mm/year), there is likely more time missing than preserved of the tectono-erosion across these different regions of Rodinia and Gondwana before Africa emerged. To further evaluate the geodynamic significance of these time gaps requires more field mapping linked to new transdisciplinary geosciences. RÉSUMÉLa région du Kango (Cango) flanque les marges nord du petit Karoo et des montagnes du Cap dans la province du Western Cape en Afrique du Sud. Elle préserve une stratigraphie condensée protérozoïque–paléozoïque exposée via une morphologie mésozoïque–cénozoïque avec une topographie actuelle de type alpin. Ses roches et ses paysages ont été cartographiés et documentés durant les 150 dernières années. Au cours des 25 dernières années, nous avons re-cartographié et daté une section du centre-est de cette région. Les roches litées de manière subverticale et clivées révèlent une stratigraphie de 8 à 10 km d'épaisseur couvrant plus de 700 millions d'années entre environ 1200 et 500 Ma avec plusieurs non-conformités et disconformités. À 252 Ma, au cours de l'orogenèse du Cap, ce Complexe du Kango s'est déformé le long de chevauchements et de plis isoclinaux produisant des schistes à fort pendage. Il a été soulevé de 3 à 5 km au cours de l'épirogenèse du Kalahari entre 140 et 60 Ma, tout en s'érodant à 100–200 m/m.a. (120–80 Ma). Pendant le Cénozoïque, le taux de soulèvement a diminué d'un ordre de grandeur et il est aujourd'hui d'environ 0,4 à 0,7 m/m.a. à travers des pentes abruptes et des canyons, contrairement à l'Himalaya où les taux d'érosion sont environ cent fois plus rapides. Une publication récente sur cette section du centre-est de la région du Kango conteste l'existence de plis isoclinaux régionaux et suggère que le dépôt des plus anciennes successions sédimentaires, y compris les roches carbonatées des Grottes du Cango (marbre calcaire avec des microfossiles énigmatiques) était simple, continu et limité entre environ 700 et 500 Ma, diminuant les estimations antérieures de la tranche d'âge stratigraphique de 60-80%. De même, des interprétations récentes des paysages complexes relient le contact nord entre les séquences rocheuses du Kango et de Table Mountain à des failles quaternaires. Nous présentons une nouvelle base de données géologiques, cartographiée à des échelles entre 1:500 et 1:10,000, et douze coupes stratigraphiques avec des directions de superposition liées à des données structurales et isotopiques qui concordent avec les répétitions le long des plis isoclinaux régionaux et des zones de chevauchement des séquences du Kango pendant l’orogenèse permo–triassique du Cap, et des données géomorphiques qui relient l'origine de ses paysages à l’altération et à l'érosion au cours de l'épirogenèse du Kalahari au Crétacé–Cénozoïque. Au cours de son évolution, le bassin du Kango flanquait les systèmes montagneux grenvillien et panafricain. Mais, à un taux de sédimentation moyen d’environ 1 mm/70 ans (0,014 mm/an) et avec les faibles taux d'érosion actuels (0,005 mm/an), il manque probablement plus d’enregistrements de la tectonique et érosion de ces différentes régions de Rodinia et Gondwana avant l'émergence de l'Afrique que ce qui est actuellement préservé. Pour évaluer la signification géodynamique de ces intervalles de temps manquant, il faut d’avantage de cartographie de terrain associée à de nouvelles géosciences transdisciplinaires.
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"The Taupo eruption, New Zealand. II. The Taupo Ignimbrite." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 314, no. 1529 (June 28, 1985): 229–310. http://dx.doi.org/10.1098/rsta.1985.0020.
Full textAbstract:
The ca. 30 km 3 Taupo ignimbrite was erupted as a climax to the ca. AD 186 Taupo eruption in the central North Island of New Zealand. It was erupted as a single vent-generated flow unit over a time period of ca. 400 s and was emplaced very rapidly (locally at more than 250-300 m s -1 ) and violently. The parent flow reached 8 0 + 10 km from source in all directions, crossed all but one of the mountains within its range and only stopped when it ran out of material. The ignimbrite is divisible into layers 1 and 2, and a distant facies which combines features of both layers. Layer 1 was generated as a result of strong fluidization in the flow head, caused by air ingestion, and consists of two main facies. Layer 1(P) is a pumiceous, mildly to strongly fines-depleted unit, generated by the expulsion of material from the flow front, and termed the jetted deposits. The overlying layer 1 (H) is a thinner, crystal- and lithic-rich, fines-depleted unit, generated by the sedimentation of coarse/dense constituents segregated out by strong fluidization within the flow head and termed the ground layer. Layer 2 consists of two facies with similar compositions but contrasting morphologies; during emplacement, material left behind by the flow body partially drained into depressions to form the valley-ponded ignimbrite, leaving the veneer deposit as a thin, landscape mantling layer on interfluves. The distant facies occurs in some outermost hilly areas of the ignimbrite where the flow velocity remained high but its volume had shrunk through deposition so that air ingestion fluidization affected the whole flow. The ignimbrite shows great lateral variations. Each facies, or variants therein, exhibits systematic degrees of development with varying distances from vent. Near vent, the flow consisted of a series of batches of material which by ca. 25 km had coalesced into a single wavy flow and by ca. 40 km into a single wave. Out to ca. 13 km, the flow was rather dilute and highly turbulent as it deflated from the collapsing eruption column. Beyond this distance it was fairly concentrated, being less than 100% expanded over its non-fluidized compacted state, and had acquired a fluidization-induced stable density stratification, which strongly suppressed turbulence in the flow body. Deflation from the eruption column was largely complete by ca. 13 km but influenced the flow as far as 20-25 km from vent. Grainsize and compositional parameters measured in the ignimbrite show lateral variations which equal or exceed the entire spectrum of published ignimbrite data. The flow had deflated and coalesced from the eruption column by ca. 20 km from vent. Beyond this distance most lateral variations are modelled by considering the flow to be a giant fluidized bed. As the flow moved, material was deposited from its base, and hence predictable vertical variations in the model fluidized bed are comparable with lateral variations in the ignimbrite. The agreement is excellent, and, in particular, discontinuities in the nature of the ignimbrite at 55-60 km from vent suggest that the more distal ignimbrite represents a vast segregation layer generated above the moving flow. Differences between the model and variations of some parameters reflect the influence of kinetic processes, such as shearing and local fluidization, that operated regardless of the bulk flow composition. The strong fluidization in the flow is a result of the high flow velocities (promoting air ingestion), not vice versa as is often accepted. Contrasts in the natures of layers 1 and 2 imply that the first material erupted contained significantly coarser, and a higher content of, lithics than the bulk of the flow. During emplacement, this earlier material was depleted by deposition and diluted by material introduced from the flow body. Systematic regional variations also occur in the ignimbrite: for example, it contains lower crystal: lithic ratios and higher density pumice in a northeasterly sector, and vice versa to the southwest. Ignimbrite found in mountainous areas shows changes consistent with its derivation from the upper, more mobile and pumiceous top of the flow. Fluidization processes generated structures and facies in the ignimbrite on various scales. Individual segregation bodies found at any exposure show features mimicking those of the ground layer, i.e. fines depletion and crystal- and lithic-enrichment. Fluidization-induced grading visible at individual exposures accounts for the great range of grading styles seen in the valley-ponded ignimbrite, and strong fluidization has locally generated an upper fines- and pumice- rich segregation layer (here termed layer 2c). On the largest scale, fluidization was primarily responsible for the generation of the layer 1 deposits, and for the grainsize and compositional zonation within the flow that produced the lateral variations in the ignimbrite. Ingested and heated air is inferred to have been the most important gas source for fluidization within the flow, although several other gas sources were locally dominant. It is clear that the thickness, grainsize and composition of the ignimbrite at any point are not simply related to values of these parameters in either the originally erupted material or the parent flow, and that, except for its density, the dimensions and composition of the parent flow cannot be directly inferred from the ignimbrite.